2617 lines
80 KiB
Python
2617 lines
80 KiB
Python
"""
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An extension of scipy.stats.stats to support masked arrays
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"""
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# Original author (2007): Pierre GF Gerard-Marchant
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# TODO : f_value_wilks_lambda looks botched... what are dfnum & dfden for ?
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# TODO : ttest_rel looks botched: what are x1,x2,v1,v2 for ?
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# TODO : reimplement ksonesamp
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from __future__ import division, print_function, absolute_import
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__all__ = ['argstoarray',
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'count_tied_groups',
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'describe',
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'f_oneway', 'find_repeats','friedmanchisquare',
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'kendalltau','kendalltau_seasonal','kruskal','kruskalwallis',
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'ks_twosamp','ks_2samp','kurtosis','kurtosistest',
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'linregress',
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'mannwhitneyu', 'meppf','mode','moment','mquantiles','msign',
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'normaltest',
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'obrientransform',
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'pearsonr','plotting_positions','pointbiserialr',
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'rankdata',
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'scoreatpercentile','sem',
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'sen_seasonal_slopes','skew','skewtest','spearmanr',
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'theilslopes','tmax','tmean','tmin','trim','trimboth',
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'trimtail','trima','trimr','trimmed_mean','trimmed_std',
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'trimmed_stde','trimmed_var','tsem','ttest_1samp','ttest_onesamp',
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'ttest_ind','ttest_rel','tvar',
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'variation',
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'winsorize',
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]
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import numpy as np
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from numpy import ndarray
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import numpy.ma as ma
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from numpy.ma import masked, nomask
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from scipy._lib.six import iteritems
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import itertools
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import warnings
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from collections import namedtuple
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from . import distributions
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import scipy.special as special
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from ._stats_mstats_common import (
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_find_repeats,
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linregress as stats_linregress,
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theilslopes as stats_theilslopes
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)
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genmissingvaldoc = """
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Notes
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-----
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Missing values are considered pair-wise: if a value is missing in x,
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the corresponding value in y is masked.
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"""
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def _chk_asarray(a, axis):
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# Always returns a masked array, raveled for axis=None
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a = ma.asanyarray(a)
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if axis is None:
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a = ma.ravel(a)
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outaxis = 0
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else:
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outaxis = axis
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return a, outaxis
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def _chk2_asarray(a, b, axis):
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a = ma.asanyarray(a)
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b = ma.asanyarray(b)
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if axis is None:
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a = ma.ravel(a)
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b = ma.ravel(b)
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outaxis = 0
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else:
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outaxis = axis
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return a, b, outaxis
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def _chk_size(a,b):
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a = ma.asanyarray(a)
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b = ma.asanyarray(b)
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(na, nb) = (a.size, b.size)
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if na != nb:
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raise ValueError("The size of the input array should match!"
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" (%s <> %s)" % (na, nb))
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return (a, b, na)
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def argstoarray(*args):
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"""
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Constructs a 2D array from a group of sequences.
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Sequences are filled with missing values to match the length of the longest
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sequence.
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Parameters
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----------
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args : sequences
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Group of sequences.
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Returns
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-------
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argstoarray : MaskedArray
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A ( `m` x `n` ) masked array, where `m` is the number of arguments and
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`n` the length of the longest argument.
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Notes
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-----
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`numpy.ma.row_stack` has identical behavior, but is called with a sequence
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of sequences.
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"""
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if len(args) == 1 and not isinstance(args[0], ndarray):
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output = ma.asarray(args[0])
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if output.ndim != 2:
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raise ValueError("The input should be 2D")
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else:
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n = len(args)
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m = max([len(k) for k in args])
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output = ma.array(np.empty((n,m), dtype=float), mask=True)
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for (k,v) in enumerate(args):
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output[k,:len(v)] = v
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output[np.logical_not(np.isfinite(output._data))] = masked
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return output
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def find_repeats(arr):
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"""Find repeats in arr and return a tuple (repeats, repeat_count).
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The input is cast to float64. Masked values are discarded.
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Parameters
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----------
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arr : sequence
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Input array. The array is flattened if it is not 1D.
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Returns
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-------
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repeats : ndarray
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Array of repeated values.
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counts : ndarray
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Array of counts.
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"""
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# Make sure we get a copy. ma.compressed promises a "new array", but can
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# actually return a reference.
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compr = np.asarray(ma.compressed(arr), dtype=np.float64)
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try:
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need_copy = np.may_share_memory(compr, arr)
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except AttributeError:
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# numpy < 1.8.2 bug: np.may_share_memory([], []) raises,
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# while in numpy 1.8.2 and above it just (correctly) returns False.
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need_copy = False
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if need_copy:
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compr = compr.copy()
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return _find_repeats(compr)
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def count_tied_groups(x, use_missing=False):
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"""
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Counts the number of tied values.
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Parameters
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----------
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x : sequence
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Sequence of data on which to counts the ties
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use_missing : bool, optional
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Whether to consider missing values as tied.
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Returns
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-------
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count_tied_groups : dict
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Returns a dictionary (nb of ties: nb of groups).
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Examples
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--------
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>>> from scipy.stats import mstats
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>>> z = [0, 0, 0, 2, 2, 2, 3, 3, 4, 5, 6]
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>>> mstats.count_tied_groups(z)
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{2: 1, 3: 2}
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In the above example, the ties were 0 (3x), 2 (3x) and 3 (2x).
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>>> z = np.ma.array([0, 0, 1, 2, 2, 2, 3, 3, 4, 5, 6])
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>>> mstats.count_tied_groups(z)
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{2: 2, 3: 1}
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>>> z[[1,-1]] = np.ma.masked
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>>> mstats.count_tied_groups(z, use_missing=True)
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{2: 2, 3: 1}
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"""
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nmasked = ma.getmask(x).sum()
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# We need the copy as find_repeats will overwrite the initial data
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data = ma.compressed(x).copy()
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(ties, counts) = find_repeats(data)
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nties = {}
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if len(ties):
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nties = dict(zip(np.unique(counts), itertools.repeat(1)))
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nties.update(dict(zip(*find_repeats(counts))))
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if nmasked and use_missing:
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try:
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nties[nmasked] += 1
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except KeyError:
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nties[nmasked] = 1
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return nties
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def rankdata(data, axis=None, use_missing=False):
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"""Returns the rank (also known as order statistics) of each data point
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along the given axis.
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If some values are tied, their rank is averaged.
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If some values are masked, their rank is set to 0 if use_missing is False,
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or set to the average rank of the unmasked values if use_missing is True.
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Parameters
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----------
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data : sequence
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Input data. The data is transformed to a masked array
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axis : {None,int}, optional
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Axis along which to perform the ranking.
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If None, the array is first flattened. An exception is raised if
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the axis is specified for arrays with a dimension larger than 2
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use_missing : bool, optional
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Whether the masked values have a rank of 0 (False) or equal to the
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average rank of the unmasked values (True).
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"""
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def _rank1d(data, use_missing=False):
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n = data.count()
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rk = np.empty(data.size, dtype=float)
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idx = data.argsort()
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rk[idx[:n]] = np.arange(1,n+1)
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if use_missing:
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rk[idx[n:]] = (n+1)/2.
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else:
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rk[idx[n:]] = 0
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repeats = find_repeats(data.copy())
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for r in repeats[0]:
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condition = (data == r).filled(False)
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rk[condition] = rk[condition].mean()
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return rk
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data = ma.array(data, copy=False)
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if axis is None:
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if data.ndim > 1:
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return _rank1d(data.ravel(), use_missing).reshape(data.shape)
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else:
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return _rank1d(data, use_missing)
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else:
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return ma.apply_along_axis(_rank1d,axis,data,use_missing).view(ndarray)
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ModeResult = namedtuple('ModeResult', ('mode', 'count'))
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def mode(a, axis=0):
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"""
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Returns an array of the modal (most common) value in the passed array.
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Parameters
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----------
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a : array_like
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n-dimensional array of which to find mode(s).
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axis : int or None, optional
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Axis along which to operate. Default is 0. If None, compute over
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the whole array `a`.
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Returns
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-------
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mode : ndarray
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Array of modal values.
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count : ndarray
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Array of counts for each mode.
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Notes
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-----
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For more details, see `stats.mode`.
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"""
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a, axis = _chk_asarray(a, axis)
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def _mode1D(a):
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(rep,cnt) = find_repeats(a)
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if not cnt.ndim:
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return (0, 0)
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elif cnt.size:
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return (rep[cnt.argmax()], cnt.max())
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else:
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not_masked_indices = ma.flatnotmasked_edges(a)
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first_not_masked_index = not_masked_indices[0]
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return (a[first_not_masked_index], 1)
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if axis is None:
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output = _mode1D(ma.ravel(a))
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output = (ma.array(output[0]), ma.array(output[1]))
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else:
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output = ma.apply_along_axis(_mode1D, axis, a)
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newshape = list(a.shape)
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newshape[axis] = 1
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slices = [slice(None)] * output.ndim
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slices[axis] = 0
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modes = output[tuple(slices)].reshape(newshape)
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slices[axis] = 1
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counts = output[tuple(slices)].reshape(newshape)
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output = (modes, counts)
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return ModeResult(*output)
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def _betai(a, b, x):
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x = np.asanyarray(x)
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x = ma.where(x < 1.0, x, 1.0) # if x > 1 then return 1.0
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return special.betainc(a, b, x)
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def msign(x):
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"""Returns the sign of x, or 0 if x is masked."""
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return ma.filled(np.sign(x), 0)
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def pearsonr(x,y):
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"""
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Calculates a Pearson correlation coefficient and the p-value for testing
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non-correlation.
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The Pearson correlation coefficient measures the linear relationship
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between two datasets. Strictly speaking, Pearson's correlation requires
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that each dataset be normally distributed. Like other correlation
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coefficients, this one varies between -1 and +1 with 0 implying no
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correlation. Correlations of -1 or +1 imply an exact linear
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relationship. Positive correlations imply that as `x` increases, so does
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`y`. Negative correlations imply that as `x` increases, `y` decreases.
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The p-value roughly indicates the probability of an uncorrelated system
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producing datasets that have a Pearson correlation at least as extreme
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as the one computed from these datasets. The p-values are not entirely
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reliable but are probably reasonable for datasets larger than 500 or so.
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Parameters
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----------
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x : 1-D array_like
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Input
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y : 1-D array_like
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Input
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Returns
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-------
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pearsonr : float
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Pearson's correlation coefficient, 2-tailed p-value.
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References
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----------
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http://www.statsoft.com/textbook/glosp.html#Pearson%20Correlation
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"""
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(x, y, n) = _chk_size(x, y)
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(x, y) = (x.ravel(), y.ravel())
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# Get the common mask and the total nb of unmasked elements
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m = ma.mask_or(ma.getmask(x), ma.getmask(y))
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n -= m.sum()
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df = n-2
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if df < 0:
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return (masked, masked)
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(mx, my) = (x.mean(), y.mean())
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(xm, ym) = (x-mx, y-my)
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r_num = ma.add.reduce(xm*ym)
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r_den = ma.sqrt(ma.dot(xm,xm) * ma.dot(ym,ym))
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r = r_num / r_den
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# Presumably, if r > 1, then it is only some small artifact of floating
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# point arithmetic.
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r = min(r, 1.0)
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r = max(r, -1.0)
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if r is masked or abs(r) == 1.0:
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prob = 0.
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else:
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t_squared = (df / ((1.0 - r) * (1.0 + r))) * r * r
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prob = _betai(0.5*df, 0.5, df/(df + t_squared))
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return r, prob
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SpearmanrResult = namedtuple('SpearmanrResult', ('correlation', 'pvalue'))
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def spearmanr(x, y, use_ties=True):
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"""
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Calculates a Spearman rank-order correlation coefficient and the p-value
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to test for non-correlation.
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The Spearman correlation is a nonparametric measure of the linear
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relationship between two datasets. Unlike the Pearson correlation, the
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Spearman correlation does not assume that both datasets are normally
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distributed. Like other correlation coefficients, this one varies
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between -1 and +1 with 0 implying no correlation. Correlations of -1 or
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+1 imply a monotonic relationship. Positive correlations imply that
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as `x` increases, so does `y`. Negative correlations imply that as `x`
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increases, `y` decreases.
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Missing values are discarded pair-wise: if a value is missing in `x`, the
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corresponding value in `y` is masked.
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The p-value roughly indicates the probability of an uncorrelated system
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producing datasets that have a Spearman correlation at least as extreme
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as the one computed from these datasets. The p-values are not entirely
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reliable but are probably reasonable for datasets larger than 500 or so.
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Parameters
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----------
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x : array_like
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The length of `x` must be > 2.
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y : array_like
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The length of `y` must be > 2.
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use_ties : bool, optional
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Whether the correction for ties should be computed.
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Returns
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-------
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correlation : float
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Spearman correlation coefficient
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pvalue : float
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2-tailed p-value.
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References
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----------
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[CRCProbStat2000] section 14.7
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"""
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(x, y, n) = _chk_size(x, y)
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(x, y) = (x.ravel(), y.ravel())
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m = ma.mask_or(ma.getmask(x), ma.getmask(y))
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# need int() here, otherwise numpy defaults to 32 bit
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# integer on all Windows architectures, causing overflow.
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# int() will keep it infinite precision.
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n -= int(m.sum())
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if m is not nomask:
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x = ma.array(x, mask=m, copy=True)
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y = ma.array(y, mask=m, copy=True)
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df = n-2
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if df < 0:
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raise ValueError("The input must have at least 3 entries!")
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# Gets the ranks and rank differences
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rankx = rankdata(x)
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ranky = rankdata(y)
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dsq = np.add.reduce((rankx-ranky)**2)
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# Tie correction
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if use_ties:
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xties = count_tied_groups(x)
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yties = count_tied_groups(y)
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corr_x = sum(v*k*(k**2-1) for (k,v) in iteritems(xties))/12.
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corr_y = sum(v*k*(k**2-1) for (k,v) in iteritems(yties))/12.
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else:
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corr_x = corr_y = 0
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denom = n*(n**2 - 1)/6.
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if corr_x != 0 or corr_y != 0:
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rho = denom - dsq - corr_x - corr_y
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rho /= ma.sqrt((denom-2*corr_x)*(denom-2*corr_y))
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else:
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rho = 1. - dsq/denom
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t = ma.sqrt(ma.divide(df,(rho+1.0)*(1.0-rho))) * rho
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if t is masked:
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prob = 0.
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else:
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prob = _betai(0.5*df, 0.5, df/(df + t * t))
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return SpearmanrResult(rho, prob)
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KendalltauResult = namedtuple('KendalltauResult', ('correlation', 'pvalue'))
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def kendalltau(x, y, use_ties=True, use_missing=False):
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"""
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Computes Kendall's rank correlation tau on two variables *x* and *y*.
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Parameters
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----------
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x : sequence
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First data list (for example, time).
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y : sequence
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Second data list.
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use_ties : {True, False}, optional
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Whether ties correction should be performed.
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use_missing : {False, True}, optional
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Whether missing data should be allocated a rank of 0 (False) or the
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average rank (True)
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Returns
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-------
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correlation : float
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Kendall tau
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pvalue : float
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Approximate 2-side p-value.
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"""
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(x, y, n) = _chk_size(x, y)
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(x, y) = (x.flatten(), y.flatten())
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m = ma.mask_or(ma.getmask(x), ma.getmask(y))
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if m is not nomask:
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x = ma.array(x, mask=m, copy=True)
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y = ma.array(y, mask=m, copy=True)
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# need int() here, otherwise numpy defaults to 32 bit
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# integer on all Windows architectures, causing overflow.
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# int() will keep it infinite precision.
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n -= int(m.sum())
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if n < 2:
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return KendalltauResult(np.nan, np.nan)
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|
|
rx = ma.masked_equal(rankdata(x, use_missing=use_missing), 0)
|
|
ry = ma.masked_equal(rankdata(y, use_missing=use_missing), 0)
|
|
idx = rx.argsort()
|
|
(rx, ry) = (rx[idx], ry[idx])
|
|
C = np.sum([((ry[i+1:] > ry[i]) * (rx[i+1:] > rx[i])).filled(0).sum()
|
|
for i in range(len(ry)-1)], dtype=float)
|
|
D = np.sum([((ry[i+1:] < ry[i])*(rx[i+1:] > rx[i])).filled(0).sum()
|
|
for i in range(len(ry)-1)], dtype=float)
|
|
if use_ties:
|
|
xties = count_tied_groups(x)
|
|
yties = count_tied_groups(y)
|
|
corr_x = np.sum([v*k*(k-1) for (k,v) in iteritems(xties)], dtype=float)
|
|
corr_y = np.sum([v*k*(k-1) for (k,v) in iteritems(yties)], dtype=float)
|
|
denom = ma.sqrt((n*(n-1)-corr_x)/2. * (n*(n-1)-corr_y)/2.)
|
|
else:
|
|
denom = n*(n-1)/2.
|
|
tau = (C-D) / denom
|
|
|
|
var_s = n*(n-1)*(2*n+5)
|
|
if use_ties:
|
|
var_s -= sum(v*k*(k-1)*(2*k+5)*1. for (k,v) in iteritems(xties))
|
|
var_s -= sum(v*k*(k-1)*(2*k+5)*1. for (k,v) in iteritems(yties))
|
|
v1 = np.sum([v*k*(k-1) for (k, v) in iteritems(xties)], dtype=float) *\
|
|
np.sum([v*k*(k-1) for (k, v) in iteritems(yties)], dtype=float)
|
|
v1 /= 2.*n*(n-1)
|
|
if n > 2:
|
|
v2 = np.sum([v*k*(k-1)*(k-2) for (k,v) in iteritems(xties)],
|
|
dtype=float) * \
|
|
np.sum([v*k*(k-1)*(k-2) for (k,v) in iteritems(yties)],
|
|
dtype=float)
|
|
v2 /= 9.*n*(n-1)*(n-2)
|
|
else:
|
|
v2 = 0
|
|
else:
|
|
v1 = v2 = 0
|
|
|
|
var_s /= 18.
|
|
var_s += (v1 + v2)
|
|
z = (C-D)/np.sqrt(var_s)
|
|
prob = special.erfc(abs(z)/np.sqrt(2))
|
|
return KendalltauResult(tau, prob)
|
|
|
|
|
|
def kendalltau_seasonal(x):
|
|
"""
|
|
Computes a multivariate Kendall's rank correlation tau, for seasonal data.
|
|
|
|
Parameters
|
|
----------
|
|
x : 2-D ndarray
|
|
Array of seasonal data, with seasons in columns.
|
|
|
|
"""
|
|
x = ma.array(x, subok=True, copy=False, ndmin=2)
|
|
(n,m) = x.shape
|
|
n_p = x.count(0)
|
|
|
|
S_szn = sum(msign(x[i:]-x[i]).sum(0) for i in range(n))
|
|
S_tot = S_szn.sum()
|
|
|
|
n_tot = x.count()
|
|
ties = count_tied_groups(x.compressed())
|
|
corr_ties = sum(v*k*(k-1) for (k,v) in iteritems(ties))
|
|
denom_tot = ma.sqrt(1.*n_tot*(n_tot-1)*(n_tot*(n_tot-1)-corr_ties))/2.
|
|
|
|
R = rankdata(x, axis=0, use_missing=True)
|
|
K = ma.empty((m,m), dtype=int)
|
|
covmat = ma.empty((m,m), dtype=float)
|
|
denom_szn = ma.empty(m, dtype=float)
|
|
for j in range(m):
|
|
ties_j = count_tied_groups(x[:,j].compressed())
|
|
corr_j = sum(v*k*(k-1) for (k,v) in iteritems(ties_j))
|
|
cmb = n_p[j]*(n_p[j]-1)
|
|
for k in range(j,m,1):
|
|
K[j,k] = sum(msign((x[i:,j]-x[i,j])*(x[i:,k]-x[i,k])).sum()
|
|
for i in range(n))
|
|
covmat[j,k] = (K[j,k] + 4*(R[:,j]*R[:,k]).sum() -
|
|
n*(n_p[j]+1)*(n_p[k]+1))/3.
|
|
K[k,j] = K[j,k]
|
|
covmat[k,j] = covmat[j,k]
|
|
|
|
denom_szn[j] = ma.sqrt(cmb*(cmb-corr_j)) / 2.
|
|
|
|
var_szn = covmat.diagonal()
|
|
|
|
z_szn = msign(S_szn) * (abs(S_szn)-1) / ma.sqrt(var_szn)
|
|
z_tot_ind = msign(S_tot) * (abs(S_tot)-1) / ma.sqrt(var_szn.sum())
|
|
z_tot_dep = msign(S_tot) * (abs(S_tot)-1) / ma.sqrt(covmat.sum())
|
|
|
|
prob_szn = special.erfc(abs(z_szn)/np.sqrt(2))
|
|
prob_tot_ind = special.erfc(abs(z_tot_ind)/np.sqrt(2))
|
|
prob_tot_dep = special.erfc(abs(z_tot_dep)/np.sqrt(2))
|
|
|
|
chi2_tot = (z_szn*z_szn).sum()
|
|
chi2_trd = m * z_szn.mean()**2
|
|
output = {'seasonal tau': S_szn/denom_szn,
|
|
'global tau': S_tot/denom_tot,
|
|
'global tau (alt)': S_tot/denom_szn.sum(),
|
|
'seasonal p-value': prob_szn,
|
|
'global p-value (indep)': prob_tot_ind,
|
|
'global p-value (dep)': prob_tot_dep,
|
|
'chi2 total': chi2_tot,
|
|
'chi2 trend': chi2_trd,
|
|
}
|
|
return output
|
|
|
|
|
|
PointbiserialrResult = namedtuple('PointbiserialrResult', ('correlation',
|
|
'pvalue'))
|
|
|
|
|
|
def pointbiserialr(x, y):
|
|
"""Calculates a point biserial correlation coefficient and its p-value.
|
|
|
|
Parameters
|
|
----------
|
|
x : array_like of bools
|
|
Input array.
|
|
y : array_like
|
|
Input array.
|
|
|
|
Returns
|
|
-------
|
|
correlation : float
|
|
R value
|
|
pvalue : float
|
|
2-tailed p-value
|
|
|
|
Notes
|
|
-----
|
|
Missing values are considered pair-wise: if a value is missing in x,
|
|
the corresponding value in y is masked.
|
|
|
|
For more details on `pointbiserialr`, see `stats.pointbiserialr`.
|
|
|
|
"""
|
|
x = ma.fix_invalid(x, copy=True).astype(bool)
|
|
y = ma.fix_invalid(y, copy=True).astype(float)
|
|
# Get rid of the missing data
|
|
m = ma.mask_or(ma.getmask(x), ma.getmask(y))
|
|
if m is not nomask:
|
|
unmask = np.logical_not(m)
|
|
x = x[unmask]
|
|
y = y[unmask]
|
|
|
|
n = len(x)
|
|
# phat is the fraction of x values that are True
|
|
phat = x.sum() / float(n)
|
|
y0 = y[~x] # y-values where x is False
|
|
y1 = y[x] # y-values where x is True
|
|
y0m = y0.mean()
|
|
y1m = y1.mean()
|
|
|
|
rpb = (y1m - y0m)*np.sqrt(phat * (1-phat)) / y.std()
|
|
|
|
df = n-2
|
|
t = rpb*ma.sqrt(df/(1.0-rpb**2))
|
|
prob = _betai(0.5*df, 0.5, df/(df+t*t))
|
|
|
|
return PointbiserialrResult(rpb, prob)
|
|
|
|
|
|
LinregressResult = namedtuple('LinregressResult', ('slope', 'intercept',
|
|
'rvalue', 'pvalue',
|
|
'stderr'))
|
|
|
|
|
|
def linregress(x, y=None):
|
|
"""
|
|
Linear regression calculation
|
|
|
|
Note that the non-masked version is used, and that this docstring is
|
|
replaced by the non-masked docstring + some info on missing data.
|
|
|
|
"""
|
|
if y is None:
|
|
x = ma.array(x)
|
|
if x.shape[0] == 2:
|
|
x, y = x
|
|
elif x.shape[1] == 2:
|
|
x, y = x.T
|
|
else:
|
|
msg = ("If only `x` is given as input, it has to be of shape "
|
|
"(2, N) or (N, 2), provided shape was %s" % str(x.shape))
|
|
raise ValueError(msg)
|
|
else:
|
|
x = ma.array(x)
|
|
y = ma.array(y)
|
|
|
|
x = x.flatten()
|
|
y = y.flatten()
|
|
|
|
m = ma.mask_or(ma.getmask(x), ma.getmask(y), shrink=False)
|
|
if m is not nomask:
|
|
x = ma.array(x, mask=m)
|
|
y = ma.array(y, mask=m)
|
|
if np.any(~m):
|
|
slope, intercept, r, prob, sterrest = stats_linregress(x.data[~m],
|
|
y.data[~m])
|
|
else:
|
|
# All data is masked
|
|
return None, None, None, None, None
|
|
else:
|
|
slope, intercept, r, prob, sterrest = stats_linregress(x.data, y.data)
|
|
|
|
return LinregressResult(slope, intercept, r, prob, sterrest)
|
|
|
|
|
|
if stats_linregress.__doc__:
|
|
linregress.__doc__ = stats_linregress.__doc__ + genmissingvaldoc
|
|
|
|
|
|
def theilslopes(y, x=None, alpha=0.95):
|
|
r"""
|
|
Computes the Theil-Sen estimator for a set of points (x, y).
|
|
|
|
`theilslopes` implements a method for robust linear regression. It
|
|
computes the slope as the median of all slopes between paired values.
|
|
|
|
Parameters
|
|
----------
|
|
y : array_like
|
|
Dependent variable.
|
|
x : array_like or None, optional
|
|
Independent variable. If None, use ``arange(len(y))`` instead.
|
|
alpha : float, optional
|
|
Confidence degree between 0 and 1. Default is 95% confidence.
|
|
Note that `alpha` is symmetric around 0.5, i.e. both 0.1 and 0.9 are
|
|
interpreted as "find the 90% confidence interval".
|
|
|
|
Returns
|
|
-------
|
|
medslope : float
|
|
Theil slope.
|
|
medintercept : float
|
|
Intercept of the Theil line, as ``median(y) - medslope*median(x)``.
|
|
lo_slope : float
|
|
Lower bound of the confidence interval on `medslope`.
|
|
up_slope : float
|
|
Upper bound of the confidence interval on `medslope`.
|
|
|
|
Notes
|
|
-----
|
|
For more details on `theilslopes`, see `stats.theilslopes`.
|
|
|
|
"""
|
|
y = ma.asarray(y).flatten()
|
|
if x is None:
|
|
x = ma.arange(len(y), dtype=float)
|
|
else:
|
|
x = ma.asarray(x).flatten()
|
|
if len(x) != len(y):
|
|
raise ValueError("Incompatible lengths ! (%s<>%s)" % (len(y),len(x)))
|
|
|
|
m = ma.mask_or(ma.getmask(x), ma.getmask(y))
|
|
y._mask = x._mask = m
|
|
# Disregard any masked elements of x or y
|
|
y = y.compressed()
|
|
x = x.compressed().astype(float)
|
|
# We now have unmasked arrays so can use `stats.theilslopes`
|
|
return stats_theilslopes(y, x, alpha=alpha)
|
|
|
|
|
|
def sen_seasonal_slopes(x):
|
|
x = ma.array(x, subok=True, copy=False, ndmin=2)
|
|
(n,_) = x.shape
|
|
# Get list of slopes per season
|
|
szn_slopes = ma.vstack([(x[i+1:]-x[i])/np.arange(1,n-i)[:,None]
|
|
for i in range(n)])
|
|
szn_medslopes = ma.median(szn_slopes, axis=0)
|
|
medslope = ma.median(szn_slopes, axis=None)
|
|
return szn_medslopes, medslope
|
|
|
|
|
|
Ttest_1sampResult = namedtuple('Ttest_1sampResult', ('statistic', 'pvalue'))
|
|
|
|
|
|
def ttest_1samp(a, popmean, axis=0):
|
|
"""
|
|
Calculates the T-test for the mean of ONE group of scores.
|
|
|
|
Parameters
|
|
----------
|
|
a : array_like
|
|
sample observation
|
|
popmean : float or array_like
|
|
expected value in null hypothesis, if array_like than it must have the
|
|
same shape as `a` excluding the axis dimension
|
|
axis : int or None, optional
|
|
Axis along which to compute test. If None, compute over the whole
|
|
array `a`.
|
|
|
|
Returns
|
|
-------
|
|
statistic : float or array
|
|
t-statistic
|
|
pvalue : float or array
|
|
two-tailed p-value
|
|
|
|
Notes
|
|
-----
|
|
For more details on `ttest_1samp`, see `stats.ttest_1samp`.
|
|
|
|
"""
|
|
a, axis = _chk_asarray(a, axis)
|
|
if a.size == 0:
|
|
return (np.nan, np.nan)
|
|
|
|
x = a.mean(axis=axis)
|
|
v = a.var(axis=axis, ddof=1)
|
|
n = a.count(axis=axis)
|
|
# force df to be an array for masked division not to throw a warning
|
|
df = ma.asanyarray(n - 1.0)
|
|
svar = ((n - 1.0) * v) / df
|
|
with np.errstate(divide='ignore', invalid='ignore'):
|
|
t = (x - popmean) / ma.sqrt(svar / n)
|
|
prob = special.betainc(0.5*df, 0.5, df/(df + t*t))
|
|
|
|
return Ttest_1sampResult(t, prob)
|
|
|
|
|
|
ttest_onesamp = ttest_1samp
|
|
|
|
|
|
Ttest_indResult = namedtuple('Ttest_indResult', ('statistic', 'pvalue'))
|
|
|
|
|
|
def ttest_ind(a, b, axis=0, equal_var=True):
|
|
"""
|
|
Calculates the T-test for the means of TWO INDEPENDENT samples of scores.
|
|
|
|
Parameters
|
|
----------
|
|
a, b : array_like
|
|
The arrays must have the same shape, except in the dimension
|
|
corresponding to `axis` (the first, by default).
|
|
axis : int or None, optional
|
|
Axis along which to compute test. If None, compute over the whole
|
|
arrays, `a`, and `b`.
|
|
equal_var : bool, optional
|
|
If True, perform a standard independent 2 sample test that assumes equal
|
|
population variances.
|
|
If False, perform Welch's t-test, which does not assume equal population
|
|
variance.
|
|
.. versionadded:: 0.17.0
|
|
|
|
Returns
|
|
-------
|
|
statistic : float or array
|
|
The calculated t-statistic.
|
|
pvalue : float or array
|
|
The two-tailed p-value.
|
|
|
|
Notes
|
|
-----
|
|
For more details on `ttest_ind`, see `stats.ttest_ind`.
|
|
|
|
"""
|
|
a, b, axis = _chk2_asarray(a, b, axis)
|
|
|
|
if a.size == 0 or b.size == 0:
|
|
return Ttest_indResult(np.nan, np.nan)
|
|
|
|
(x1, x2) = (a.mean(axis), b.mean(axis))
|
|
(v1, v2) = (a.var(axis=axis, ddof=1), b.var(axis=axis, ddof=1))
|
|
(n1, n2) = (a.count(axis), b.count(axis))
|
|
|
|
if equal_var:
|
|
# force df to be an array for masked division not to throw a warning
|
|
df = ma.asanyarray(n1 + n2 - 2.0)
|
|
svar = ((n1-1)*v1+(n2-1)*v2) / df
|
|
denom = ma.sqrt(svar*(1.0/n1 + 1.0/n2)) # n-D computation here!
|
|
else:
|
|
vn1 = v1/n1
|
|
vn2 = v2/n2
|
|
with np.errstate(divide='ignore', invalid='ignore'):
|
|
df = (vn1 + vn2)**2 / (vn1**2 / (n1 - 1) + vn2**2 / (n2 - 1))
|
|
|
|
# If df is undefined, variances are zero.
|
|
# It doesn't matter what df is as long as it is not NaN.
|
|
df = np.where(np.isnan(df), 1, df)
|
|
denom = ma.sqrt(vn1 + vn2)
|
|
|
|
with np.errstate(divide='ignore', invalid='ignore'):
|
|
t = (x1-x2) / denom
|
|
probs = special.betainc(0.5*df, 0.5, df/(df + t*t)).reshape(t.shape)
|
|
|
|
return Ttest_indResult(t, probs.squeeze())
|
|
|
|
|
|
Ttest_relResult = namedtuple('Ttest_relResult', ('statistic', 'pvalue'))
|
|
|
|
|
|
def ttest_rel(a, b, axis=0):
|
|
"""
|
|
Calculates the T-test on TWO RELATED samples of scores, a and b.
|
|
|
|
Parameters
|
|
----------
|
|
a, b : array_like
|
|
The arrays must have the same shape.
|
|
axis : int or None, optional
|
|
Axis along which to compute test. If None, compute over the whole
|
|
arrays, `a`, and `b`.
|
|
|
|
Returns
|
|
-------
|
|
statistic : float or array
|
|
t-statistic
|
|
pvalue : float or array
|
|
two-tailed p-value
|
|
|
|
Notes
|
|
-----
|
|
For more details on `ttest_rel`, see `stats.ttest_rel`.
|
|
|
|
"""
|
|
a, b, axis = _chk2_asarray(a, b, axis)
|
|
if len(a) != len(b):
|
|
raise ValueError('unequal length arrays')
|
|
|
|
if a.size == 0 or b.size == 0:
|
|
return Ttest_relResult(np.nan, np.nan)
|
|
|
|
n = a.count(axis)
|
|
df = ma.asanyarray(n-1.0)
|
|
d = (a-b).astype('d')
|
|
dm = d.mean(axis)
|
|
v = d.var(axis=axis, ddof=1)
|
|
denom = ma.sqrt(v / n)
|
|
with np.errstate(divide='ignore', invalid='ignore'):
|
|
t = dm / denom
|
|
|
|
probs = special.betainc(0.5*df, 0.5, df/(df + t*t)).reshape(t.shape).squeeze()
|
|
|
|
return Ttest_relResult(t, probs)
|
|
|
|
|
|
MannwhitneyuResult = namedtuple('MannwhitneyuResult', ('statistic',
|
|
'pvalue'))
|
|
|
|
|
|
def mannwhitneyu(x,y, use_continuity=True):
|
|
"""
|
|
Computes the Mann-Whitney statistic
|
|
|
|
Missing values in `x` and/or `y` are discarded.
|
|
|
|
Parameters
|
|
----------
|
|
x : sequence
|
|
Input
|
|
y : sequence
|
|
Input
|
|
use_continuity : {True, False}, optional
|
|
Whether a continuity correction (1/2.) should be taken into account.
|
|
|
|
Returns
|
|
-------
|
|
statistic : float
|
|
The Mann-Whitney statistics
|
|
pvalue : float
|
|
Approximate p-value assuming a normal distribution.
|
|
|
|
"""
|
|
x = ma.asarray(x).compressed().view(ndarray)
|
|
y = ma.asarray(y).compressed().view(ndarray)
|
|
ranks = rankdata(np.concatenate([x,y]))
|
|
(nx, ny) = (len(x), len(y))
|
|
nt = nx + ny
|
|
U = ranks[:nx].sum() - nx*(nx+1)/2.
|
|
U = max(U, nx*ny - U)
|
|
u = nx*ny - U
|
|
|
|
mu = (nx*ny)/2.
|
|
sigsq = (nt**3 - nt)/12.
|
|
ties = count_tied_groups(ranks)
|
|
sigsq -= sum(v*(k**3-k) for (k,v) in iteritems(ties))/12.
|
|
sigsq *= nx*ny/float(nt*(nt-1))
|
|
|
|
if use_continuity:
|
|
z = (U - 1/2. - mu) / ma.sqrt(sigsq)
|
|
else:
|
|
z = (U - mu) / ma.sqrt(sigsq)
|
|
|
|
prob = special.erfc(abs(z)/np.sqrt(2))
|
|
return MannwhitneyuResult(u, prob)
|
|
|
|
|
|
KruskalResult = namedtuple('KruskalResult', ('statistic', 'pvalue'))
|
|
|
|
|
|
def kruskal(*args):
|
|
"""
|
|
Compute the Kruskal-Wallis H-test for independent samples
|
|
|
|
Parameters
|
|
----------
|
|
sample1, sample2, ... : array_like
|
|
Two or more arrays with the sample measurements can be given as
|
|
arguments.
|
|
|
|
Returns
|
|
-------
|
|
statistic : float
|
|
The Kruskal-Wallis H statistic, corrected for ties
|
|
pvalue : float
|
|
The p-value for the test using the assumption that H has a chi
|
|
square distribution
|
|
|
|
Notes
|
|
-----
|
|
For more details on `kruskal`, see `stats.kruskal`.
|
|
|
|
"""
|
|
output = argstoarray(*args)
|
|
ranks = ma.masked_equal(rankdata(output, use_missing=False), 0)
|
|
sumrk = ranks.sum(-1)
|
|
ngrp = ranks.count(-1)
|
|
ntot = ranks.count()
|
|
H = 12./(ntot*(ntot+1)) * (sumrk**2/ngrp).sum() - 3*(ntot+1)
|
|
# Tie correction
|
|
ties = count_tied_groups(ranks)
|
|
T = 1. - sum(v*(k**3-k) for (k,v) in iteritems(ties))/float(ntot**3-ntot)
|
|
if T == 0:
|
|
raise ValueError('All numbers are identical in kruskal')
|
|
|
|
H /= T
|
|
df = len(output) - 1
|
|
prob = distributions.chi2.sf(H, df)
|
|
return KruskalResult(H, prob)
|
|
|
|
|
|
kruskalwallis = kruskal
|
|
|
|
|
|
def ks_twosamp(data1, data2, alternative="two-sided"):
|
|
"""
|
|
Computes the Kolmogorov-Smirnov test on two samples.
|
|
|
|
Missing values are discarded.
|
|
|
|
Parameters
|
|
----------
|
|
data1 : array_like
|
|
First data set
|
|
data2 : array_like
|
|
Second data set
|
|
alternative : {'two-sided', 'less', 'greater'}, optional
|
|
Indicates the alternative hypothesis. Default is 'two-sided'.
|
|
|
|
Returns
|
|
-------
|
|
d : float
|
|
Value of the Kolmogorov Smirnov test
|
|
p : float
|
|
Corresponding p-value.
|
|
|
|
"""
|
|
(data1, data2) = (ma.asarray(data1), ma.asarray(data2))
|
|
(n1, n2) = (data1.count(), data2.count())
|
|
n = (n1*n2/float(n1+n2))
|
|
mix = ma.concatenate((data1.compressed(), data2.compressed()))
|
|
mixsort = mix.argsort(kind='mergesort')
|
|
csum = np.where(mixsort < n1, 1./n1, -1./n2).cumsum()
|
|
# Check for ties
|
|
if len(np.unique(mix)) < (n1+n2):
|
|
csum = csum[np.r_[np.diff(mix[mixsort]).nonzero()[0],-1]]
|
|
|
|
alternative = str(alternative).lower()[0]
|
|
if alternative == 't':
|
|
d = ma.abs(csum).max()
|
|
prob = special.kolmogorov(np.sqrt(n)*d)
|
|
elif alternative == 'l':
|
|
d = -csum.min()
|
|
prob = np.exp(-2*n*d**2)
|
|
elif alternative == 'g':
|
|
d = csum.max()
|
|
prob = np.exp(-2*n*d**2)
|
|
else:
|
|
raise ValueError("Invalid value for the alternative hypothesis: "
|
|
"should be in 'two-sided', 'less' or 'greater'")
|
|
|
|
return (d, prob)
|
|
|
|
|
|
ks_2samp = ks_twosamp
|
|
|
|
|
|
def trima(a, limits=None, inclusive=(True,True)):
|
|
"""
|
|
Trims an array by masking the data outside some given limits.
|
|
|
|
Returns a masked version of the input array.
|
|
|
|
Parameters
|
|
----------
|
|
a : array_like
|
|
Input array.
|
|
limits : {None, tuple}, optional
|
|
Tuple of (lower limit, upper limit) in absolute values.
|
|
Values of the input array lower (greater) than the lower (upper) limit
|
|
will be masked. A limit is None indicates an open interval.
|
|
inclusive : (bool, bool) tuple, optional
|
|
Tuple of (lower flag, upper flag), indicating whether values exactly
|
|
equal to the lower (upper) limit are allowed.
|
|
|
|
"""
|
|
a = ma.asarray(a)
|
|
a.unshare_mask()
|
|
if (limits is None) or (limits == (None, None)):
|
|
return a
|
|
|
|
(lower_lim, upper_lim) = limits
|
|
(lower_in, upper_in) = inclusive
|
|
condition = False
|
|
if lower_lim is not None:
|
|
if lower_in:
|
|
condition |= (a < lower_lim)
|
|
else:
|
|
condition |= (a <= lower_lim)
|
|
|
|
if upper_lim is not None:
|
|
if upper_in:
|
|
condition |= (a > upper_lim)
|
|
else:
|
|
condition |= (a >= upper_lim)
|
|
|
|
a[condition.filled(True)] = masked
|
|
return a
|
|
|
|
|
|
def trimr(a, limits=None, inclusive=(True, True), axis=None):
|
|
"""
|
|
Trims an array by masking some proportion of the data on each end.
|
|
Returns a masked version of the input array.
|
|
|
|
Parameters
|
|
----------
|
|
a : sequence
|
|
Input array.
|
|
limits : {None, tuple}, optional
|
|
Tuple of the percentages to cut on each side of the array, with respect
|
|
to the number of unmasked data, as floats between 0. and 1.
|
|
Noting n the number of unmasked data before trimming, the
|
|
(n*limits[0])th smallest data and the (n*limits[1])th largest data are
|
|
masked, and the total number of unmasked data after trimming is
|
|
n*(1.-sum(limits)). The value of one limit can be set to None to
|
|
indicate an open interval.
|
|
inclusive : {(True,True) tuple}, optional
|
|
Tuple of flags indicating whether the number of data being masked on
|
|
the left (right) end should be truncated (True) or rounded (False) to
|
|
integers.
|
|
axis : {None,int}, optional
|
|
Axis along which to trim. If None, the whole array is trimmed, but its
|
|
shape is maintained.
|
|
|
|
"""
|
|
def _trimr1D(a, low_limit, up_limit, low_inclusive, up_inclusive):
|
|
n = a.count()
|
|
idx = a.argsort()
|
|
if low_limit:
|
|
if low_inclusive:
|
|
lowidx = int(low_limit*n)
|
|
else:
|
|
lowidx = np.round(low_limit*n)
|
|
a[idx[:lowidx]] = masked
|
|
if up_limit is not None:
|
|
if up_inclusive:
|
|
upidx = n - int(n*up_limit)
|
|
else:
|
|
upidx = n - np.round(n*up_limit)
|
|
a[idx[upidx:]] = masked
|
|
return a
|
|
|
|
a = ma.asarray(a)
|
|
a.unshare_mask()
|
|
if limits is None:
|
|
return a
|
|
|
|
# Check the limits
|
|
(lolim, uplim) = limits
|
|
errmsg = "The proportion to cut from the %s should be between 0. and 1."
|
|
if lolim is not None:
|
|
if lolim > 1. or lolim < 0:
|
|
raise ValueError(errmsg % 'beginning' + "(got %s)" % lolim)
|
|
if uplim is not None:
|
|
if uplim > 1. or uplim < 0:
|
|
raise ValueError(errmsg % 'end' + "(got %s)" % uplim)
|
|
|
|
(loinc, upinc) = inclusive
|
|
|
|
if axis is None:
|
|
shp = a.shape
|
|
return _trimr1D(a.ravel(),lolim,uplim,loinc,upinc).reshape(shp)
|
|
else:
|
|
return ma.apply_along_axis(_trimr1D, axis, a, lolim,uplim,loinc,upinc)
|
|
|
|
|
|
trimdoc = """
|
|
Parameters
|
|
----------
|
|
a : sequence
|
|
Input array
|
|
limits : {None, tuple}, optional
|
|
If `relative` is False, tuple (lower limit, upper limit) in absolute values.
|
|
Values of the input array lower (greater) than the lower (upper) limit are
|
|
masked.
|
|
|
|
If `relative` is True, tuple (lower percentage, upper percentage) to cut
|
|
on each side of the array, with respect to the number of unmasked data.
|
|
|
|
Noting n the number of unmasked data before trimming, the (n*limits[0])th
|
|
smallest data and the (n*limits[1])th largest data are masked, and the
|
|
total number of unmasked data after trimming is n*(1.-sum(limits))
|
|
In each case, the value of one limit can be set to None to indicate an
|
|
open interval.
|
|
|
|
If limits is None, no trimming is performed
|
|
inclusive : {(bool, bool) tuple}, optional
|
|
If `relative` is False, tuple indicating whether values exactly equal
|
|
to the absolute limits are allowed.
|
|
If `relative` is True, tuple indicating whether the number of data
|
|
being masked on each side should be rounded (True) or truncated
|
|
(False).
|
|
relative : bool, optional
|
|
Whether to consider the limits as absolute values (False) or proportions
|
|
to cut (True).
|
|
axis : int, optional
|
|
Axis along which to trim.
|
|
"""
|
|
|
|
|
|
def trim(a, limits=None, inclusive=(True,True), relative=False, axis=None):
|
|
"""
|
|
Trims an array by masking the data outside some given limits.
|
|
|
|
Returns a masked version of the input array.
|
|
|
|
%s
|
|
|
|
Examples
|
|
--------
|
|
>>> from scipy.stats.mstats import trim
|
|
>>> z = [ 1, 2, 3, 4, 5, 6, 7, 8, 9,10]
|
|
>>> print(trim(z,(3,8)))
|
|
[-- -- 3 4 5 6 7 8 -- --]
|
|
>>> print(trim(z,(0.1,0.2),relative=True))
|
|
[-- 2 3 4 5 6 7 8 -- --]
|
|
|
|
"""
|
|
if relative:
|
|
return trimr(a, limits=limits, inclusive=inclusive, axis=axis)
|
|
else:
|
|
return trima(a, limits=limits, inclusive=inclusive)
|
|
|
|
|
|
if trim.__doc__ is not None:
|
|
trim.__doc__ = trim.__doc__ % trimdoc
|
|
|
|
|
|
def trimboth(data, proportiontocut=0.2, inclusive=(True,True), axis=None):
|
|
"""
|
|
Trims the smallest and largest data values.
|
|
|
|
Trims the `data` by masking the ``int(proportiontocut * n)`` smallest and
|
|
``int(proportiontocut * n)`` largest values of data along the given axis,
|
|
where n is the number of unmasked values before trimming.
|
|
|
|
Parameters
|
|
----------
|
|
data : ndarray
|
|
Data to trim.
|
|
proportiontocut : float, optional
|
|
Percentage of trimming (as a float between 0 and 1).
|
|
If n is the number of unmasked values before trimming, the number of
|
|
values after trimming is ``(1 - 2*proportiontocut) * n``.
|
|
Default is 0.2.
|
|
inclusive : {(bool, bool) tuple}, optional
|
|
Tuple indicating whether the number of data being masked on each side
|
|
should be rounded (True) or truncated (False).
|
|
axis : int, optional
|
|
Axis along which to perform the trimming.
|
|
If None, the input array is first flattened.
|
|
|
|
"""
|
|
return trimr(data, limits=(proportiontocut,proportiontocut),
|
|
inclusive=inclusive, axis=axis)
|
|
|
|
|
|
def trimtail(data, proportiontocut=0.2, tail='left', inclusive=(True,True),
|
|
axis=None):
|
|
"""
|
|
Trims the data by masking values from one tail.
|
|
|
|
Parameters
|
|
----------
|
|
data : array_like
|
|
Data to trim.
|
|
proportiontocut : float, optional
|
|
Percentage of trimming. If n is the number of unmasked values
|
|
before trimming, the number of values after trimming is
|
|
``(1 - proportiontocut) * n``. Default is 0.2.
|
|
tail : {'left','right'}, optional
|
|
If 'left' the `proportiontocut` lowest values will be masked.
|
|
If 'right' the `proportiontocut` highest values will be masked.
|
|
Default is 'left'.
|
|
inclusive : {(bool, bool) tuple}, optional
|
|
Tuple indicating whether the number of data being masked on each side
|
|
should be rounded (True) or truncated (False). Default is
|
|
(True, True).
|
|
axis : int, optional
|
|
Axis along which to perform the trimming.
|
|
If None, the input array is first flattened. Default is None.
|
|
|
|
Returns
|
|
-------
|
|
trimtail : ndarray
|
|
Returned array of same shape as `data` with masked tail values.
|
|
|
|
"""
|
|
tail = str(tail).lower()[0]
|
|
if tail == 'l':
|
|
limits = (proportiontocut,None)
|
|
elif tail == 'r':
|
|
limits = (None, proportiontocut)
|
|
else:
|
|
raise TypeError("The tail argument should be in ('left','right')")
|
|
|
|
return trimr(data, limits=limits, axis=axis, inclusive=inclusive)
|
|
|
|
|
|
trim1 = trimtail
|
|
|
|
|
|
def trimmed_mean(a, limits=(0.1,0.1), inclusive=(1,1), relative=True,
|
|
axis=None):
|
|
"""Returns the trimmed mean of the data along the given axis.
|
|
|
|
%s
|
|
|
|
""" % trimdoc
|
|
if (not isinstance(limits,tuple)) and isinstance(limits,float):
|
|
limits = (limits, limits)
|
|
if relative:
|
|
return trimr(a,limits=limits,inclusive=inclusive,axis=axis).mean(axis=axis)
|
|
else:
|
|
return trima(a,limits=limits,inclusive=inclusive).mean(axis=axis)
|
|
|
|
|
|
def trimmed_var(a, limits=(0.1,0.1), inclusive=(1,1), relative=True,
|
|
axis=None, ddof=0):
|
|
"""Returns the trimmed variance of the data along the given axis.
|
|
|
|
%s
|
|
ddof : {0,integer}, optional
|
|
Means Delta Degrees of Freedom. The denominator used during computations
|
|
is (n-ddof). DDOF=0 corresponds to a biased estimate, DDOF=1 to an un-
|
|
biased estimate of the variance.
|
|
|
|
""" % trimdoc
|
|
if (not isinstance(limits,tuple)) and isinstance(limits,float):
|
|
limits = (limits, limits)
|
|
if relative:
|
|
out = trimr(a,limits=limits, inclusive=inclusive,axis=axis)
|
|
else:
|
|
out = trima(a,limits=limits,inclusive=inclusive)
|
|
|
|
return out.var(axis=axis, ddof=ddof)
|
|
|
|
|
|
def trimmed_std(a, limits=(0.1,0.1), inclusive=(1,1), relative=True,
|
|
axis=None, ddof=0):
|
|
"""Returns the trimmed standard deviation of the data along the given axis.
|
|
|
|
%s
|
|
ddof : {0,integer}, optional
|
|
Means Delta Degrees of Freedom. The denominator used during computations
|
|
is (n-ddof). DDOF=0 corresponds to a biased estimate, DDOF=1 to an un-
|
|
biased estimate of the variance.
|
|
|
|
""" % trimdoc
|
|
if (not isinstance(limits,tuple)) and isinstance(limits,float):
|
|
limits = (limits, limits)
|
|
if relative:
|
|
out = trimr(a,limits=limits,inclusive=inclusive,axis=axis)
|
|
else:
|
|
out = trima(a,limits=limits,inclusive=inclusive)
|
|
return out.std(axis=axis,ddof=ddof)
|
|
|
|
|
|
def trimmed_stde(a, limits=(0.1,0.1), inclusive=(1,1), axis=None):
|
|
"""
|
|
Returns the standard error of the trimmed mean along the given axis.
|
|
|
|
Parameters
|
|
----------
|
|
a : sequence
|
|
Input array
|
|
limits : {(0.1,0.1), tuple of float}, optional
|
|
tuple (lower percentage, upper percentage) to cut on each side of the
|
|
array, with respect to the number of unmasked data.
|
|
|
|
If n is the number of unmasked data before trimming, the values
|
|
smaller than ``n * limits[0]`` and the values larger than
|
|
``n * `limits[1]`` are masked, and the total number of unmasked
|
|
data after trimming is ``n * (1.-sum(limits))``. In each case,
|
|
the value of one limit can be set to None to indicate an open interval.
|
|
If `limits` is None, no trimming is performed.
|
|
inclusive : {(bool, bool) tuple} optional
|
|
Tuple indicating whether the number of data being masked on each side
|
|
should be rounded (True) or truncated (False).
|
|
axis : int, optional
|
|
Axis along which to trim.
|
|
|
|
Returns
|
|
-------
|
|
trimmed_stde : scalar or ndarray
|
|
|
|
"""
|
|
def _trimmed_stde_1D(a, low_limit, up_limit, low_inclusive, up_inclusive):
|
|
"Returns the standard error of the trimmed mean for a 1D input data."
|
|
n = a.count()
|
|
idx = a.argsort()
|
|
if low_limit:
|
|
if low_inclusive:
|
|
lowidx = int(low_limit*n)
|
|
else:
|
|
lowidx = np.round(low_limit*n)
|
|
a[idx[:lowidx]] = masked
|
|
if up_limit is not None:
|
|
if up_inclusive:
|
|
upidx = n - int(n*up_limit)
|
|
else:
|
|
upidx = n - np.round(n*up_limit)
|
|
a[idx[upidx:]] = masked
|
|
a[idx[:lowidx]] = a[idx[lowidx]]
|
|
a[idx[upidx:]] = a[idx[upidx-1]]
|
|
winstd = a.std(ddof=1)
|
|
return winstd / ((1-low_limit-up_limit)*np.sqrt(len(a)))
|
|
|
|
a = ma.array(a, copy=True, subok=True)
|
|
a.unshare_mask()
|
|
if limits is None:
|
|
return a.std(axis=axis,ddof=1)/ma.sqrt(a.count(axis))
|
|
if (not isinstance(limits,tuple)) and isinstance(limits,float):
|
|
limits = (limits, limits)
|
|
|
|
# Check the limits
|
|
(lolim, uplim) = limits
|
|
errmsg = "The proportion to cut from the %s should be between 0. and 1."
|
|
if lolim is not None:
|
|
if lolim > 1. or lolim < 0:
|
|
raise ValueError(errmsg % 'beginning' + "(got %s)" % lolim)
|
|
if uplim is not None:
|
|
if uplim > 1. or uplim < 0:
|
|
raise ValueError(errmsg % 'end' + "(got %s)" % uplim)
|
|
|
|
(loinc, upinc) = inclusive
|
|
if (axis is None):
|
|
return _trimmed_stde_1D(a.ravel(),lolim,uplim,loinc,upinc)
|
|
else:
|
|
if a.ndim > 2:
|
|
raise ValueError("Array 'a' must be at most two dimensional, but got a.ndim = %d" % a.ndim)
|
|
return ma.apply_along_axis(_trimmed_stde_1D, axis, a,
|
|
lolim,uplim,loinc,upinc)
|
|
|
|
|
|
def _mask_to_limits(a, limits, inclusive):
|
|
"""Mask an array for values outside of given limits.
|
|
|
|
This is primarily a utility function.
|
|
|
|
Parameters
|
|
----------
|
|
a : array
|
|
limits : (float or None, float or None)
|
|
A tuple consisting of the (lower limit, upper limit). Values in the
|
|
input array less than the lower limit or greater than the upper limit
|
|
will be masked out. None implies no limit.
|
|
inclusive : (bool, bool)
|
|
A tuple consisting of the (lower flag, upper flag). These flags
|
|
determine whether values exactly equal to lower or upper are allowed.
|
|
|
|
Returns
|
|
-------
|
|
A MaskedArray.
|
|
|
|
Raises
|
|
------
|
|
A ValueError if there are no values within the given limits.
|
|
"""
|
|
lower_limit, upper_limit = limits
|
|
lower_include, upper_include = inclusive
|
|
am = ma.MaskedArray(a)
|
|
if lower_limit is not None:
|
|
if lower_include:
|
|
am = ma.masked_less(am, lower_limit)
|
|
else:
|
|
am = ma.masked_less_equal(am, lower_limit)
|
|
|
|
if upper_limit is not None:
|
|
if upper_include:
|
|
am = ma.masked_greater(am, upper_limit)
|
|
else:
|
|
am = ma.masked_greater_equal(am, upper_limit)
|
|
|
|
if am.count() == 0:
|
|
raise ValueError("No array values within given limits")
|
|
|
|
return am
|
|
|
|
|
|
def tmean(a, limits=None, inclusive=(True, True), axis=None):
|
|
"""
|
|
Compute the trimmed mean.
|
|
|
|
Parameters
|
|
----------
|
|
a : array_like
|
|
Array of values.
|
|
limits : None or (lower limit, upper limit), optional
|
|
Values in the input array less than the lower limit or greater than the
|
|
upper limit will be ignored. When limits is None (default), then all
|
|
values are used. Either of the limit values in the tuple can also be
|
|
None representing a half-open interval.
|
|
inclusive : (bool, bool), optional
|
|
A tuple consisting of the (lower flag, upper flag). These flags
|
|
determine whether values exactly equal to the lower or upper limits
|
|
are included. The default value is (True, True).
|
|
axis : int or None, optional
|
|
Axis along which to operate. If None, compute over the
|
|
whole array. Default is None.
|
|
|
|
Returns
|
|
-------
|
|
tmean : float
|
|
|
|
Notes
|
|
-----
|
|
For more details on `tmean`, see `stats.tmean`.
|
|
|
|
"""
|
|
return trima(a, limits=limits, inclusive=inclusive).mean(axis=axis)
|
|
|
|
|
|
def tvar(a, limits=None, inclusive=(True, True), axis=0, ddof=1):
|
|
"""
|
|
Compute the trimmed variance
|
|
|
|
This function computes the sample variance of an array of values,
|
|
while ignoring values which are outside of given `limits`.
|
|
|
|
Parameters
|
|
----------
|
|
a : array_like
|
|
Array of values.
|
|
limits : None or (lower limit, upper limit), optional
|
|
Values in the input array less than the lower limit or greater than the
|
|
upper limit will be ignored. When limits is None, then all values are
|
|
used. Either of the limit values in the tuple can also be None
|
|
representing a half-open interval. The default value is None.
|
|
inclusive : (bool, bool), optional
|
|
A tuple consisting of the (lower flag, upper flag). These flags
|
|
determine whether values exactly equal to the lower or upper limits
|
|
are included. The default value is (True, True).
|
|
axis : int or None, optional
|
|
Axis along which to operate. If None, compute over the
|
|
whole array. Default is zero.
|
|
ddof : int, optional
|
|
Delta degrees of freedom. Default is 1.
|
|
|
|
Returns
|
|
-------
|
|
tvar : float
|
|
Trimmed variance.
|
|
|
|
Notes
|
|
-----
|
|
For more details on `tvar`, see `stats.tvar`.
|
|
|
|
"""
|
|
a = a.astype(float).ravel()
|
|
if limits is None:
|
|
n = (~a.mask).sum() # todo: better way to do that?
|
|
return np.ma.var(a) * n/(n-1.)
|
|
am = _mask_to_limits(a, limits=limits, inclusive=inclusive)
|
|
|
|
return np.ma.var(am, axis=axis, ddof=ddof)
|
|
|
|
|
|
def tmin(a, lowerlimit=None, axis=0, inclusive=True):
|
|
"""
|
|
Compute the trimmed minimum
|
|
|
|
Parameters
|
|
----------
|
|
a : array_like
|
|
array of values
|
|
lowerlimit : None or float, optional
|
|
Values in the input array less than the given limit will be ignored.
|
|
When lowerlimit is None, then all values are used. The default value
|
|
is None.
|
|
axis : int or None, optional
|
|
Axis along which to operate. Default is 0. If None, compute over the
|
|
whole array `a`.
|
|
inclusive : {True, False}, optional
|
|
This flag determines whether values exactly equal to the lower limit
|
|
are included. The default value is True.
|
|
|
|
Returns
|
|
-------
|
|
tmin : float, int or ndarray
|
|
|
|
Notes
|
|
-----
|
|
For more details on `tmin`, see `stats.tmin`.
|
|
|
|
"""
|
|
a, axis = _chk_asarray(a, axis)
|
|
am = trima(a, (lowerlimit, None), (inclusive, False))
|
|
return ma.minimum.reduce(am, axis)
|
|
|
|
|
|
def tmax(a, upperlimit=None, axis=0, inclusive=True):
|
|
"""
|
|
Compute the trimmed maximum
|
|
|
|
This function computes the maximum value of an array along a given axis,
|
|
while ignoring values larger than a specified upper limit.
|
|
|
|
Parameters
|
|
----------
|
|
a : array_like
|
|
array of values
|
|
upperlimit : None or float, optional
|
|
Values in the input array greater than the given limit will be ignored.
|
|
When upperlimit is None, then all values are used. The default value
|
|
is None.
|
|
axis : int or None, optional
|
|
Axis along which to operate. Default is 0. If None, compute over the
|
|
whole array `a`.
|
|
inclusive : {True, False}, optional
|
|
This flag determines whether values exactly equal to the upper limit
|
|
are included. The default value is True.
|
|
|
|
Returns
|
|
-------
|
|
tmax : float, int or ndarray
|
|
|
|
Notes
|
|
-----
|
|
For more details on `tmax`, see `stats.tmax`.
|
|
|
|
"""
|
|
a, axis = _chk_asarray(a, axis)
|
|
am = trima(a, (None, upperlimit), (False, inclusive))
|
|
return ma.maximum.reduce(am, axis)
|
|
|
|
|
|
def tsem(a, limits=None, inclusive=(True, True), axis=0, ddof=1):
|
|
"""
|
|
Compute the trimmed standard error of the mean.
|
|
|
|
This function finds the standard error of the mean for given
|
|
values, ignoring values outside the given `limits`.
|
|
|
|
Parameters
|
|
----------
|
|
a : array_like
|
|
array of values
|
|
limits : None or (lower limit, upper limit), optional
|
|
Values in the input array less than the lower limit or greater than the
|
|
upper limit will be ignored. When limits is None, then all values are
|
|
used. Either of the limit values in the tuple can also be None
|
|
representing a half-open interval. The default value is None.
|
|
inclusive : (bool, bool), optional
|
|
A tuple consisting of the (lower flag, upper flag). These flags
|
|
determine whether values exactly equal to the lower or upper limits
|
|
are included. The default value is (True, True).
|
|
axis : int or None, optional
|
|
Axis along which to operate. If None, compute over the
|
|
whole array. Default is zero.
|
|
ddof : int, optional
|
|
Delta degrees of freedom. Default is 1.
|
|
|
|
Returns
|
|
-------
|
|
tsem : float
|
|
|
|
Notes
|
|
-----
|
|
For more details on `tsem`, see `stats.tsem`.
|
|
|
|
"""
|
|
a = ma.asarray(a).ravel()
|
|
if limits is None:
|
|
n = float(a.count())
|
|
return a.std(axis=axis, ddof=ddof)/ma.sqrt(n)
|
|
|
|
am = trima(a.ravel(), limits, inclusive)
|
|
sd = np.sqrt(am.var(axis=axis, ddof=ddof))
|
|
return sd / np.sqrt(am.count())
|
|
|
|
|
|
def winsorize(a, limits=None, inclusive=(True, True), inplace=False,
|
|
axis=None):
|
|
"""Returns a Winsorized version of the input array.
|
|
|
|
The (limits[0])th lowest values are set to the (limits[0])th percentile,
|
|
and the (limits[1])th highest values are set to the (1 - limits[1])th
|
|
percentile.
|
|
Masked values are skipped.
|
|
|
|
|
|
Parameters
|
|
----------
|
|
a : sequence
|
|
Input array.
|
|
limits : {None, tuple of float}, optional
|
|
Tuple of the percentages to cut on each side of the array, with respect
|
|
to the number of unmasked data, as floats between 0. and 1.
|
|
Noting n the number of unmasked data before trimming, the
|
|
(n*limits[0])th smallest data and the (n*limits[1])th largest data are
|
|
masked, and the total number of unmasked data after trimming
|
|
is n*(1.-sum(limits)) The value of one limit can be set to None to
|
|
indicate an open interval.
|
|
inclusive : {(True, True) tuple}, optional
|
|
Tuple indicating whether the number of data being masked on each side
|
|
should be truncated (True) or rounded (False).
|
|
inplace : {False, True}, optional
|
|
Whether to winsorize in place (True) or to use a copy (False)
|
|
axis : {None, int}, optional
|
|
Axis along which to trim. If None, the whole array is trimmed, but its
|
|
shape is maintained.
|
|
|
|
Notes
|
|
-----
|
|
This function is applied to reduce the effect of possibly spurious outliers
|
|
by limiting the extreme values.
|
|
|
|
"""
|
|
def _winsorize1D(a, low_limit, up_limit, low_include, up_include):
|
|
n = a.count()
|
|
idx = a.argsort()
|
|
if low_limit:
|
|
if low_include:
|
|
lowidx = int(low_limit * n)
|
|
else:
|
|
lowidx = np.round(low_limit * n).astype(int)
|
|
a[idx[:lowidx]] = a[idx[lowidx]]
|
|
if up_limit is not None:
|
|
if up_include:
|
|
upidx = n - int(n * up_limit)
|
|
else:
|
|
upidx = n - np.round(n * up_limit).astype(int)
|
|
a[idx[upidx:]] = a[idx[upidx - 1]]
|
|
return a
|
|
|
|
# We are going to modify a: better make a copy
|
|
a = ma.array(a, copy=np.logical_not(inplace))
|
|
|
|
if limits is None:
|
|
return a
|
|
if (not isinstance(limits, tuple)) and isinstance(limits, float):
|
|
limits = (limits, limits)
|
|
|
|
# Check the limits
|
|
(lolim, uplim) = limits
|
|
errmsg = "The proportion to cut from the %s should be between 0. and 1."
|
|
if lolim is not None:
|
|
if lolim > 1. or lolim < 0:
|
|
raise ValueError(errmsg % 'beginning' + "(got %s)" % lolim)
|
|
if uplim is not None:
|
|
if uplim > 1. or uplim < 0:
|
|
raise ValueError(errmsg % 'end' + "(got %s)" % uplim)
|
|
|
|
(loinc, upinc) = inclusive
|
|
|
|
if axis is None:
|
|
shp = a.shape
|
|
return _winsorize1D(a.ravel(), lolim, uplim, loinc, upinc).reshape(shp)
|
|
else:
|
|
return ma.apply_along_axis(_winsorize1D, axis, a, lolim, uplim, loinc,
|
|
upinc)
|
|
|
|
|
|
def moment(a, moment=1, axis=0):
|
|
"""
|
|
Calculates the nth moment about the mean for a sample.
|
|
|
|
Parameters
|
|
----------
|
|
a : array_like
|
|
data
|
|
moment : int, optional
|
|
order of central moment that is returned
|
|
axis : int or None, optional
|
|
Axis along which the central moment is computed. Default is 0.
|
|
If None, compute over the whole array `a`.
|
|
|
|
Returns
|
|
-------
|
|
n-th central moment : ndarray or float
|
|
The appropriate moment along the given axis or over all values if axis
|
|
is None. The denominator for the moment calculation is the number of
|
|
observations, no degrees of freedom correction is done.
|
|
|
|
Notes
|
|
-----
|
|
For more details about `moment`, see `stats.moment`.
|
|
|
|
"""
|
|
a, axis = _chk_asarray(a, axis)
|
|
if moment == 1:
|
|
# By definition the first moment about the mean is 0.
|
|
shape = list(a.shape)
|
|
del shape[axis]
|
|
if shape:
|
|
# return an actual array of the appropriate shape
|
|
return np.zeros(shape, dtype=float)
|
|
else:
|
|
# the input was 1D, so return a scalar instead of a rank-0 array
|
|
return np.float64(0.0)
|
|
else:
|
|
# Exponentiation by squares: form exponent sequence
|
|
n_list = [moment]
|
|
current_n = moment
|
|
while current_n > 2:
|
|
if current_n % 2:
|
|
current_n = (current_n-1)/2
|
|
else:
|
|
current_n /= 2
|
|
n_list.append(current_n)
|
|
|
|
# Starting point for exponentiation by squares
|
|
a_zero_mean = a - ma.expand_dims(a.mean(axis), axis)
|
|
if n_list[-1] == 1:
|
|
s = a_zero_mean.copy()
|
|
else:
|
|
s = a_zero_mean**2
|
|
|
|
# Perform multiplications
|
|
for n in n_list[-2::-1]:
|
|
s = s**2
|
|
if n % 2:
|
|
s *= a_zero_mean
|
|
return s.mean(axis)
|
|
|
|
|
|
def variation(a, axis=0):
|
|
"""
|
|
Computes the coefficient of variation, the ratio of the biased standard
|
|
deviation to the mean.
|
|
|
|
Parameters
|
|
----------
|
|
a : array_like
|
|
Input array.
|
|
axis : int or None, optional
|
|
Axis along which to calculate the coefficient of variation. Default
|
|
is 0. If None, compute over the whole array `a`.
|
|
|
|
Returns
|
|
-------
|
|
variation : ndarray
|
|
The calculated variation along the requested axis.
|
|
|
|
Notes
|
|
-----
|
|
For more details about `variation`, see `stats.variation`.
|
|
|
|
"""
|
|
a, axis = _chk_asarray(a, axis)
|
|
return a.std(axis)/a.mean(axis)
|
|
|
|
|
|
def skew(a, axis=0, bias=True):
|
|
"""
|
|
Computes the skewness of a data set.
|
|
|
|
Parameters
|
|
----------
|
|
a : ndarray
|
|
data
|
|
axis : int or None, optional
|
|
Axis along which skewness is calculated. Default is 0.
|
|
If None, compute over the whole array `a`.
|
|
bias : bool, optional
|
|
If False, then the calculations are corrected for statistical bias.
|
|
|
|
Returns
|
|
-------
|
|
skewness : ndarray
|
|
The skewness of values along an axis, returning 0 where all values are
|
|
equal.
|
|
|
|
Notes
|
|
-----
|
|
For more details about `skew`, see `stats.skew`.
|
|
|
|
"""
|
|
a, axis = _chk_asarray(a,axis)
|
|
n = a.count(axis)
|
|
m2 = moment(a, 2, axis)
|
|
m3 = moment(a, 3, axis)
|
|
olderr = np.seterr(all='ignore')
|
|
try:
|
|
vals = ma.where(m2 == 0, 0, m3 / m2**1.5)
|
|
finally:
|
|
np.seterr(**olderr)
|
|
|
|
if not bias:
|
|
can_correct = (n > 2) & (m2 > 0)
|
|
if can_correct.any():
|
|
m2 = np.extract(can_correct, m2)
|
|
m3 = np.extract(can_correct, m3)
|
|
nval = ma.sqrt((n-1.0)*n)/(n-2.0)*m3/m2**1.5
|
|
np.place(vals, can_correct, nval)
|
|
return vals
|
|
|
|
|
|
def kurtosis(a, axis=0, fisher=True, bias=True):
|
|
"""
|
|
Computes the kurtosis (Fisher or Pearson) of a dataset.
|
|
|
|
Kurtosis is the fourth central moment divided by the square of the
|
|
variance. If Fisher's definition is used, then 3.0 is subtracted from
|
|
the result to give 0.0 for a normal distribution.
|
|
|
|
If bias is False then the kurtosis is calculated using k statistics to
|
|
eliminate bias coming from biased moment estimators
|
|
|
|
Use `kurtosistest` to see if result is close enough to normal.
|
|
|
|
Parameters
|
|
----------
|
|
a : array
|
|
data for which the kurtosis is calculated
|
|
axis : int or None, optional
|
|
Axis along which the kurtosis is calculated. Default is 0.
|
|
If None, compute over the whole array `a`.
|
|
fisher : bool, optional
|
|
If True, Fisher's definition is used (normal ==> 0.0). If False,
|
|
Pearson's definition is used (normal ==> 3.0).
|
|
bias : bool, optional
|
|
If False, then the calculations are corrected for statistical bias.
|
|
|
|
Returns
|
|
-------
|
|
kurtosis : array
|
|
The kurtosis of values along an axis. If all values are equal,
|
|
return -3 for Fisher's definition and 0 for Pearson's definition.
|
|
|
|
Notes
|
|
-----
|
|
For more details about `kurtosis`, see `stats.kurtosis`.
|
|
|
|
"""
|
|
a, axis = _chk_asarray(a, axis)
|
|
m2 = moment(a, 2, axis)
|
|
m4 = moment(a, 4, axis)
|
|
olderr = np.seterr(all='ignore')
|
|
try:
|
|
vals = ma.where(m2 == 0, 0, m4 / m2**2.0)
|
|
finally:
|
|
np.seterr(**olderr)
|
|
|
|
if not bias:
|
|
n = a.count(axis)
|
|
can_correct = (n > 3) & (m2 is not ma.masked and m2 > 0)
|
|
if can_correct.any():
|
|
n = np.extract(can_correct, n)
|
|
m2 = np.extract(can_correct, m2)
|
|
m4 = np.extract(can_correct, m4)
|
|
nval = 1.0/(n-2)/(n-3)*((n*n-1.0)*m4/m2**2.0-3*(n-1)**2.0)
|
|
np.place(vals, can_correct, nval+3.0)
|
|
if fisher:
|
|
return vals - 3
|
|
else:
|
|
return vals
|
|
|
|
|
|
DescribeResult = namedtuple('DescribeResult', ('nobs', 'minmax', 'mean',
|
|
'variance', 'skewness',
|
|
'kurtosis'))
|
|
|
|
|
|
def describe(a, axis=0, ddof=0, bias=True):
|
|
"""
|
|
Computes several descriptive statistics of the passed array.
|
|
|
|
Parameters
|
|
----------
|
|
a : array_like
|
|
Data array
|
|
axis : int or None, optional
|
|
Axis along which to calculate statistics. Default 0. If None,
|
|
compute over the whole array `a`.
|
|
ddof : int, optional
|
|
degree of freedom (default 0); note that default ddof is different
|
|
from the same routine in stats.describe
|
|
bias : bool, optional
|
|
If False, then the skewness and kurtosis calculations are corrected for
|
|
statistical bias.
|
|
|
|
Returns
|
|
-------
|
|
nobs : int
|
|
(size of the data (discarding missing values)
|
|
|
|
minmax : (int, int)
|
|
min, max
|
|
|
|
mean : float
|
|
arithmetic mean
|
|
|
|
variance : float
|
|
unbiased variance
|
|
|
|
skewness : float
|
|
biased skewness
|
|
|
|
kurtosis : float
|
|
biased kurtosis
|
|
|
|
Examples
|
|
--------
|
|
>>> from scipy.stats.mstats import describe
|
|
>>> ma = np.ma.array(range(6), mask=[0, 0, 0, 1, 1, 1])
|
|
>>> describe(ma)
|
|
DescribeResult(nobs=3, minmax=(masked_array(data=0,
|
|
mask=False,
|
|
fill_value=999999), masked_array(data=2,
|
|
mask=False,
|
|
fill_value=999999)), mean=1.0, variance=0.6666666666666666,
|
|
skewness=masked_array(data=0., mask=False, fill_value=1e+20),
|
|
kurtosis=-1.5)
|
|
|
|
"""
|
|
a, axis = _chk_asarray(a, axis)
|
|
n = a.count(axis)
|
|
mm = (ma.minimum.reduce(a), ma.maximum.reduce(a))
|
|
m = a.mean(axis)
|
|
v = a.var(axis, ddof=ddof)
|
|
sk = skew(a, axis, bias=bias)
|
|
kurt = kurtosis(a, axis, bias=bias)
|
|
|
|
return DescribeResult(n, mm, m, v, sk, kurt)
|
|
|
|
|
|
def stde_median(data, axis=None):
|
|
"""Returns the McKean-Schrader estimate of the standard error of the sample
|
|
median along the given axis. masked values are discarded.
|
|
|
|
Parameters
|
|
----------
|
|
data : ndarray
|
|
Data to trim.
|
|
axis : {None,int}, optional
|
|
Axis along which to perform the trimming.
|
|
If None, the input array is first flattened.
|
|
|
|
"""
|
|
def _stdemed_1D(data):
|
|
data = np.sort(data.compressed())
|
|
n = len(data)
|
|
z = 2.5758293035489004
|
|
k = int(np.round((n+1)/2. - z * np.sqrt(n/4.),0))
|
|
return ((data[n-k] - data[k-1])/(2.*z))
|
|
|
|
data = ma.array(data, copy=False, subok=True)
|
|
if (axis is None):
|
|
return _stdemed_1D(data)
|
|
else:
|
|
if data.ndim > 2:
|
|
raise ValueError("Array 'data' must be at most two dimensional, "
|
|
"but got data.ndim = %d" % data.ndim)
|
|
return ma.apply_along_axis(_stdemed_1D, axis, data)
|
|
|
|
|
|
SkewtestResult = namedtuple('SkewtestResult', ('statistic', 'pvalue'))
|
|
|
|
|
|
def skewtest(a, axis=0):
|
|
"""
|
|
Tests whether the skew is different from the normal distribution.
|
|
|
|
Parameters
|
|
----------
|
|
a : array
|
|
The data to be tested
|
|
axis : int or None, optional
|
|
Axis along which statistics are calculated. Default is 0.
|
|
If None, compute over the whole array `a`.
|
|
|
|
Returns
|
|
-------
|
|
statistic : float
|
|
The computed z-score for this test.
|
|
pvalue : float
|
|
a 2-sided p-value for the hypothesis test
|
|
|
|
Notes
|
|
-----
|
|
For more details about `skewtest`, see `stats.skewtest`.
|
|
|
|
"""
|
|
a, axis = _chk_asarray(a, axis)
|
|
if axis is None:
|
|
a = a.ravel()
|
|
axis = 0
|
|
b2 = skew(a,axis)
|
|
n = a.count(axis)
|
|
if np.min(n) < 8:
|
|
raise ValueError(
|
|
"skewtest is not valid with less than 8 samples; %i samples"
|
|
" were given." % np.min(n))
|
|
|
|
y = b2 * ma.sqrt(((n+1)*(n+3)) / (6.0*(n-2)))
|
|
beta2 = (3.0*(n*n+27*n-70)*(n+1)*(n+3)) / ((n-2.0)*(n+5)*(n+7)*(n+9))
|
|
W2 = -1 + ma.sqrt(2*(beta2-1))
|
|
delta = 1/ma.sqrt(0.5*ma.log(W2))
|
|
alpha = ma.sqrt(2.0/(W2-1))
|
|
y = ma.where(y == 0, 1, y)
|
|
Z = delta*ma.log(y/alpha + ma.sqrt((y/alpha)**2+1))
|
|
|
|
return SkewtestResult(Z, 2 * distributions.norm.sf(np.abs(Z)))
|
|
|
|
|
|
KurtosistestResult = namedtuple('KurtosistestResult', ('statistic',
|
|
'pvalue'))
|
|
|
|
|
|
def kurtosistest(a, axis=0):
|
|
"""
|
|
Tests whether a dataset has normal kurtosis
|
|
|
|
Parameters
|
|
----------
|
|
a : array
|
|
array of the sample data
|
|
axis : int or None, optional
|
|
Axis along which to compute test. Default is 0. If None,
|
|
compute over the whole array `a`.
|
|
|
|
Returns
|
|
-------
|
|
statistic : float
|
|
The computed z-score for this test.
|
|
pvalue : float
|
|
The 2-sided p-value for the hypothesis test
|
|
|
|
Notes
|
|
-----
|
|
For more details about `kurtosistest`, see `stats.kurtosistest`.
|
|
|
|
"""
|
|
a, axis = _chk_asarray(a, axis)
|
|
n = a.count(axis=axis)
|
|
if np.min(n) < 5:
|
|
raise ValueError(
|
|
"kurtosistest requires at least 5 observations; %i observations"
|
|
" were given." % np.min(n))
|
|
if np.min(n) < 20:
|
|
warnings.warn(
|
|
"kurtosistest only valid for n>=20 ... continuing anyway, n=%i" %
|
|
np.min(n))
|
|
|
|
b2 = kurtosis(a, axis, fisher=False)
|
|
E = 3.0*(n-1) / (n+1)
|
|
varb2 = 24.0*n*(n-2.)*(n-3) / ((n+1)*(n+1.)*(n+3)*(n+5))
|
|
x = (b2-E)/ma.sqrt(varb2)
|
|
sqrtbeta1 = 6.0*(n*n-5*n+2)/((n+7)*(n+9)) * np.sqrt((6.0*(n+3)*(n+5)) /
|
|
(n*(n-2)*(n-3)))
|
|
A = 6.0 + 8.0/sqrtbeta1 * (2.0/sqrtbeta1 + np.sqrt(1+4.0/(sqrtbeta1**2)))
|
|
term1 = 1 - 2./(9.0*A)
|
|
denom = 1 + x*ma.sqrt(2/(A-4.0))
|
|
if np.ma.isMaskedArray(denom):
|
|
# For multi-dimensional array input
|
|
denom[denom < 0] = masked
|
|
elif denom < 0:
|
|
denom = masked
|
|
|
|
term2 = ma.power((1-2.0/A)/denom,1/3.0)
|
|
Z = (term1 - term2) / np.sqrt(2/(9.0*A))
|
|
|
|
return KurtosistestResult(Z, 2 * distributions.norm.sf(np.abs(Z)))
|
|
|
|
|
|
NormaltestResult = namedtuple('NormaltestResult', ('statistic', 'pvalue'))
|
|
|
|
|
|
def normaltest(a, axis=0):
|
|
"""
|
|
Tests whether a sample differs from a normal distribution.
|
|
|
|
Parameters
|
|
----------
|
|
a : array_like
|
|
The array containing the data to be tested.
|
|
axis : int or None, optional
|
|
Axis along which to compute test. Default is 0. If None,
|
|
compute over the whole array `a`.
|
|
|
|
Returns
|
|
-------
|
|
statistic : float or array
|
|
``s^2 + k^2``, where ``s`` is the z-score returned by `skewtest` and
|
|
``k`` is the z-score returned by `kurtosistest`.
|
|
pvalue : float or array
|
|
A 2-sided chi squared probability for the hypothesis test.
|
|
|
|
Notes
|
|
-----
|
|
For more details about `normaltest`, see `stats.normaltest`.
|
|
|
|
"""
|
|
a, axis = _chk_asarray(a, axis)
|
|
s, _ = skewtest(a, axis)
|
|
k, _ = kurtosistest(a, axis)
|
|
k2 = s*s + k*k
|
|
|
|
return NormaltestResult(k2, distributions.chi2.sf(k2, 2))
|
|
|
|
|
|
def mquantiles(a, prob=list([.25,.5,.75]), alphap=.4, betap=.4, axis=None,
|
|
limit=()):
|
|
"""
|
|
Computes empirical quantiles for a data array.
|
|
|
|
Samples quantile are defined by ``Q(p) = (1-gamma)*x[j] + gamma*x[j+1]``,
|
|
where ``x[j]`` is the j-th order statistic, and gamma is a function of
|
|
``j = floor(n*p + m)``, ``m = alphap + p*(1 - alphap - betap)`` and
|
|
``g = n*p + m - j``.
|
|
|
|
Reinterpreting the above equations to compare to **R** lead to the
|
|
equation: ``p(k) = (k - alphap)/(n + 1 - alphap - betap)``
|
|
|
|
Typical values of (alphap,betap) are:
|
|
- (0,1) : ``p(k) = k/n`` : linear interpolation of cdf
|
|
(**R** type 4)
|
|
- (.5,.5) : ``p(k) = (k - 1/2.)/n`` : piecewise linear function
|
|
(**R** type 5)
|
|
- (0,0) : ``p(k) = k/(n+1)`` :
|
|
(**R** type 6)
|
|
- (1,1) : ``p(k) = (k-1)/(n-1)``: p(k) = mode[F(x[k])].
|
|
(**R** type 7, **R** default)
|
|
- (1/3,1/3): ``p(k) = (k-1/3)/(n+1/3)``: Then p(k) ~ median[F(x[k])].
|
|
The resulting quantile estimates are approximately median-unbiased
|
|
regardless of the distribution of x.
|
|
(**R** type 8)
|
|
- (3/8,3/8): ``p(k) = (k-3/8)/(n+1/4)``: Blom.
|
|
The resulting quantile estimates are approximately unbiased
|
|
if x is normally distributed
|
|
(**R** type 9)
|
|
- (.4,.4) : approximately quantile unbiased (Cunnane)
|
|
- (.35,.35): APL, used with PWM
|
|
|
|
Parameters
|
|
----------
|
|
a : array_like
|
|
Input data, as a sequence or array of dimension at most 2.
|
|
prob : array_like, optional
|
|
List of quantiles to compute.
|
|
alphap : float, optional
|
|
Plotting positions parameter, default is 0.4.
|
|
betap : float, optional
|
|
Plotting positions parameter, default is 0.4.
|
|
axis : int, optional
|
|
Axis along which to perform the trimming.
|
|
If None (default), the input array is first flattened.
|
|
limit : tuple, optional
|
|
Tuple of (lower, upper) values.
|
|
Values of `a` outside this open interval are ignored.
|
|
|
|
Returns
|
|
-------
|
|
mquantiles : MaskedArray
|
|
An array containing the calculated quantiles.
|
|
|
|
Notes
|
|
-----
|
|
This formulation is very similar to **R** except the calculation of
|
|
``m`` from ``alphap`` and ``betap``, where in **R** ``m`` is defined
|
|
with each type.
|
|
|
|
References
|
|
----------
|
|
.. [1] *R* statistical software: http://www.r-project.org/
|
|
.. [2] *R* ``quantile`` function:
|
|
http://stat.ethz.ch/R-manual/R-devel/library/stats/html/quantile.html
|
|
|
|
Examples
|
|
--------
|
|
>>> from scipy.stats.mstats import mquantiles
|
|
>>> a = np.array([6., 47., 49., 15., 42., 41., 7., 39., 43., 40., 36.])
|
|
>>> mquantiles(a)
|
|
array([ 19.2, 40. , 42.8])
|
|
|
|
Using a 2D array, specifying axis and limit.
|
|
|
|
>>> data = np.array([[ 6., 7., 1.],
|
|
... [ 47., 15., 2.],
|
|
... [ 49., 36., 3.],
|
|
... [ 15., 39., 4.],
|
|
... [ 42., 40., -999.],
|
|
... [ 41., 41., -999.],
|
|
... [ 7., -999., -999.],
|
|
... [ 39., -999., -999.],
|
|
... [ 43., -999., -999.],
|
|
... [ 40., -999., -999.],
|
|
... [ 36., -999., -999.]])
|
|
>>> print(mquantiles(data, axis=0, limit=(0, 50)))
|
|
[[19.2 14.6 1.45]
|
|
[40. 37.5 2.5 ]
|
|
[42.8 40.05 3.55]]
|
|
|
|
>>> data[:, 2] = -999.
|
|
>>> print(mquantiles(data, axis=0, limit=(0, 50)))
|
|
[[19.200000000000003 14.6 --]
|
|
[40.0 37.5 --]
|
|
[42.800000000000004 40.05 --]]
|
|
|
|
"""
|
|
def _quantiles1D(data,m,p):
|
|
x = np.sort(data.compressed())
|
|
n = len(x)
|
|
if n == 0:
|
|
return ma.array(np.empty(len(p), dtype=float), mask=True)
|
|
elif n == 1:
|
|
return ma.array(np.resize(x, p.shape), mask=nomask)
|
|
aleph = (n*p + m)
|
|
k = np.floor(aleph.clip(1, n-1)).astype(int)
|
|
gamma = (aleph-k).clip(0,1)
|
|
return (1.-gamma)*x[(k-1).tolist()] + gamma*x[k.tolist()]
|
|
|
|
data = ma.array(a, copy=False)
|
|
if data.ndim > 2:
|
|
raise TypeError("Array should be 2D at most !")
|
|
|
|
if limit:
|
|
condition = (limit[0] < data) & (data < limit[1])
|
|
data[~condition.filled(True)] = masked
|
|
|
|
p = np.array(prob, copy=False, ndmin=1)
|
|
m = alphap + p*(1.-alphap-betap)
|
|
# Computes quantiles along axis (or globally)
|
|
if (axis is None):
|
|
return _quantiles1D(data, m, p)
|
|
|
|
return ma.apply_along_axis(_quantiles1D, axis, data, m, p)
|
|
|
|
|
|
def scoreatpercentile(data, per, limit=(), alphap=.4, betap=.4):
|
|
"""Calculate the score at the given 'per' percentile of the
|
|
sequence a. For example, the score at per=50 is the median.
|
|
|
|
This function is a shortcut to mquantile
|
|
|
|
"""
|
|
if (per < 0) or (per > 100.):
|
|
raise ValueError("The percentile should be between 0. and 100. !"
|
|
" (got %s)" % per)
|
|
|
|
return mquantiles(data, prob=[per/100.], alphap=alphap, betap=betap,
|
|
limit=limit, axis=0).squeeze()
|
|
|
|
|
|
def plotting_positions(data, alpha=0.4, beta=0.4):
|
|
"""
|
|
Returns plotting positions (or empirical percentile points) for the data.
|
|
|
|
Plotting positions are defined as ``(i-alpha)/(n+1-alpha-beta)``, where:
|
|
- i is the rank order statistics
|
|
- n is the number of unmasked values along the given axis
|
|
- `alpha` and `beta` are two parameters.
|
|
|
|
Typical values for `alpha` and `beta` are:
|
|
- (0,1) : ``p(k) = k/n``, linear interpolation of cdf (R, type 4)
|
|
- (.5,.5) : ``p(k) = (k-1/2.)/n``, piecewise linear function
|
|
(R, type 5)
|
|
- (0,0) : ``p(k) = k/(n+1)``, Weibull (R type 6)
|
|
- (1,1) : ``p(k) = (k-1)/(n-1)``, in this case,
|
|
``p(k) = mode[F(x[k])]``. That's R default (R type 7)
|
|
- (1/3,1/3): ``p(k) = (k-1/3)/(n+1/3)``, then
|
|
``p(k) ~ median[F(x[k])]``.
|
|
The resulting quantile estimates are approximately median-unbiased
|
|
regardless of the distribution of x. (R type 8)
|
|
- (3/8,3/8): ``p(k) = (k-3/8)/(n+1/4)``, Blom.
|
|
The resulting quantile estimates are approximately unbiased
|
|
if x is normally distributed (R type 9)
|
|
- (.4,.4) : approximately quantile unbiased (Cunnane)
|
|
- (.35,.35): APL, used with PWM
|
|
- (.3175, .3175): used in scipy.stats.probplot
|
|
|
|
Parameters
|
|
----------
|
|
data : array_like
|
|
Input data, as a sequence or array of dimension at most 2.
|
|
alpha : float, optional
|
|
Plotting positions parameter. Default is 0.4.
|
|
beta : float, optional
|
|
Plotting positions parameter. Default is 0.4.
|
|
|
|
Returns
|
|
-------
|
|
positions : MaskedArray
|
|
The calculated plotting positions.
|
|
|
|
"""
|
|
data = ma.array(data, copy=False).reshape(1,-1)
|
|
n = data.count()
|
|
plpos = np.empty(data.size, dtype=float)
|
|
plpos[n:] = 0
|
|
plpos[data.argsort(axis=None)[:n]] = ((np.arange(1, n+1) - alpha) /
|
|
(n + 1.0 - alpha - beta))
|
|
return ma.array(plpos, mask=data._mask)
|
|
|
|
|
|
meppf = plotting_positions
|
|
|
|
|
|
def obrientransform(*args):
|
|
"""
|
|
Computes a transform on input data (any number of columns). Used to
|
|
test for homogeneity of variance prior to running one-way stats. Each
|
|
array in ``*args`` is one level of a factor. If an `f_oneway()` run on
|
|
the transformed data and found significant, variances are unequal. From
|
|
Maxwell and Delaney, p.112.
|
|
|
|
Returns: transformed data for use in an ANOVA
|
|
"""
|
|
data = argstoarray(*args).T
|
|
v = data.var(axis=0,ddof=1)
|
|
m = data.mean(0)
|
|
n = data.count(0).astype(float)
|
|
# result = ((N-1.5)*N*(a-m)**2 - 0.5*v*(n-1))/((n-1)*(n-2))
|
|
data -= m
|
|
data **= 2
|
|
data *= (n-1.5)*n
|
|
data -= 0.5*v*(n-1)
|
|
data /= (n-1.)*(n-2.)
|
|
if not ma.allclose(v,data.mean(0)):
|
|
raise ValueError("Lack of convergence in obrientransform.")
|
|
|
|
return data
|
|
|
|
|
|
def sem(a, axis=0, ddof=1):
|
|
"""
|
|
Calculates the standard error of the mean of the input array.
|
|
|
|
Also sometimes called standard error of measurement.
|
|
|
|
Parameters
|
|
----------
|
|
a : array_like
|
|
An array containing the values for which the standard error is
|
|
returned.
|
|
axis : int or None, optional
|
|
If axis is None, ravel `a` first. If axis is an integer, this will be
|
|
the axis over which to operate. Defaults to 0.
|
|
ddof : int, optional
|
|
Delta degrees-of-freedom. How many degrees of freedom to adjust
|
|
for bias in limited samples relative to the population estimate
|
|
of variance. Defaults to 1.
|
|
|
|
Returns
|
|
-------
|
|
s : ndarray or float
|
|
The standard error of the mean in the sample(s), along the input axis.
|
|
|
|
Notes
|
|
-----
|
|
The default value for `ddof` changed in scipy 0.15.0 to be consistent with
|
|
`stats.sem` as well as with the most common definition used (like in the R
|
|
documentation).
|
|
|
|
Examples
|
|
--------
|
|
Find standard error along the first axis:
|
|
|
|
>>> from scipy import stats
|
|
>>> a = np.arange(20).reshape(5,4)
|
|
>>> print(stats.mstats.sem(a))
|
|
[2.8284271247461903 2.8284271247461903 2.8284271247461903
|
|
2.8284271247461903]
|
|
|
|
Find standard error across the whole array, using n degrees of freedom:
|
|
|
|
>>> print(stats.mstats.sem(a, axis=None, ddof=0))
|
|
1.2893796958227628
|
|
|
|
"""
|
|
a, axis = _chk_asarray(a, axis)
|
|
n = a.count(axis=axis)
|
|
s = a.std(axis=axis, ddof=ddof) / ma.sqrt(n)
|
|
return s
|
|
|
|
|
|
F_onewayResult = namedtuple('F_onewayResult', ('statistic', 'pvalue'))
|
|
|
|
|
|
def f_oneway(*args):
|
|
"""
|
|
Performs a 1-way ANOVA, returning an F-value and probability given
|
|
any number of groups. From Heiman, pp.394-7.
|
|
|
|
Usage: ``f_oneway(*args)``, where ``*args`` is 2 or more arrays,
|
|
one per treatment group.
|
|
|
|
Returns
|
|
-------
|
|
statistic : float
|
|
The computed F-value of the test.
|
|
pvalue : float
|
|
The associated p-value from the F-distribution.
|
|
|
|
"""
|
|
# Construct a single array of arguments: each row is a group
|
|
data = argstoarray(*args)
|
|
ngroups = len(data)
|
|
ntot = data.count()
|
|
sstot = (data**2).sum() - (data.sum())**2/float(ntot)
|
|
ssbg = (data.count(-1) * (data.mean(-1)-data.mean())**2).sum()
|
|
sswg = sstot-ssbg
|
|
dfbg = ngroups-1
|
|
dfwg = ntot - ngroups
|
|
msb = ssbg/float(dfbg)
|
|
msw = sswg/float(dfwg)
|
|
f = msb/msw
|
|
prob = special.fdtrc(dfbg, dfwg, f) # equivalent to stats.f.sf
|
|
|
|
return F_onewayResult(f, prob)
|
|
|
|
|
|
FriedmanchisquareResult = namedtuple('FriedmanchisquareResult',
|
|
('statistic', 'pvalue'))
|
|
|
|
|
|
def friedmanchisquare(*args):
|
|
"""Friedman Chi-Square is a non-parametric, one-way within-subjects ANOVA.
|
|
This function calculates the Friedman Chi-square test for repeated measures
|
|
and returns the result, along with the associated probability value.
|
|
|
|
Each input is considered a given group. Ideally, the number of treatments
|
|
among each group should be equal. If this is not the case, only the first
|
|
n treatments are taken into account, where n is the number of treatments
|
|
of the smallest group.
|
|
If a group has some missing values, the corresponding treatments are masked
|
|
in the other groups.
|
|
The test statistic is corrected for ties.
|
|
|
|
Masked values in one group are propagated to the other groups.
|
|
|
|
Returns
|
|
-------
|
|
statistic : float
|
|
the test statistic.
|
|
pvalue : float
|
|
the associated p-value.
|
|
|
|
"""
|
|
data = argstoarray(*args).astype(float)
|
|
k = len(data)
|
|
if k < 3:
|
|
raise ValueError("Less than 3 groups (%i): " % k +
|
|
"the Friedman test is NOT appropriate.")
|
|
|
|
ranked = ma.masked_values(rankdata(data, axis=0), 0)
|
|
if ranked._mask is not nomask:
|
|
ranked = ma.mask_cols(ranked)
|
|
ranked = ranked.compressed().reshape(k,-1).view(ndarray)
|
|
else:
|
|
ranked = ranked._data
|
|
(k,n) = ranked.shape
|
|
# Ties correction
|
|
repeats = [find_repeats(row) for row in ranked.T]
|
|
ties = np.array([y for x, y in repeats if x.size > 0])
|
|
tie_correction = 1 - (ties**3-ties).sum()/float(n*(k**3-k))
|
|
|
|
ssbg = np.sum((ranked.sum(-1) - n*(k+1)/2.)**2)
|
|
chisq = ssbg * 12./(n*k*(k+1)) * 1./tie_correction
|
|
|
|
return FriedmanchisquareResult(chisq,
|
|
distributions.chi2.sf(chisq, k-1))
|