200 lines
7.3 KiB
Python
200 lines
7.3 KiB
Python
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# Author: Hamzeh Alsalhi <ha258@cornell.edu>
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#
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# License: BSD 3 clause
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from __future__ import division
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import numpy as np
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import scipy.sparse as sp
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import array
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from sklearn.utils import check_random_state
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from ._random import sample_without_replacement
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from .deprecation import deprecated
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__all__ = ['sample_without_replacement', 'choice']
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# This is a backport of np.random.choice from numpy 1.7
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# The function can be removed when we bump the requirements to >=1.7
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@deprecated("sklearn.utils.random.choice was deprecated in version 0.19 "
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"and will be removed in 0.21. Use np.random.choice or "
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"np.random.RandomState.choice instead.")
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def choice(a, size=None, replace=True, p=None, random_state=None):
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"""
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choice(a, size=None, replace=True, p=None)
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Generates a random sample from a given 1-D array
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.. versionadded:: 1.7.0
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Parameters
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-----------
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a : 1-D array-like or int
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If an ndarray, a random sample is generated from its elements.
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If an int, the random sample is generated as if a was np.arange(n)
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size : int or tuple of ints, optional
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Output shape. Default is None, in which case a single value is
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returned.
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replace : boolean, optional
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Whether the sample is with or without replacement.
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p : 1-D array-like, optional
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The probabilities associated with each entry in a.
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If not given the sample assumes a uniform distribution over all
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entries in a.
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random_state : int, RandomState instance or None, optional (default=None)
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If int, random_state is the seed used by the random number generator;
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If RandomState instance, random_state is the random number generator;
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If None, the random number generator is the RandomState instance used
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by `np.random`.
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Returns
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--------
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samples : 1-D ndarray, shape (size,)
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The generated random samples
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Raises
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-------
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ValueError
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If a is an int and less than zero, if a or p are not 1-dimensional,
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if a is an array-like of size 0, if p is not a vector of
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probabilities, if a and p have different lengths, or if
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replace=False and the sample size is greater than the population
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size
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See Also
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---------
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randint, shuffle, permutation
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Examples
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---------
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Generate a uniform random sample from np.arange(5) of size 3:
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>>> np.random.choice(5, 3) # doctest: +SKIP
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array([0, 3, 4])
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>>> #This is equivalent to np.random.randint(0,5,3)
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Generate a non-uniform random sample from np.arange(5) of size 3:
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>>> np.random.choice(5, 3, p=[0.1, 0, 0.3, 0.6, 0]) # doctest: +SKIP
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array([3, 3, 0])
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Generate a uniform random sample from np.arange(5) of size 3 without
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replacement:
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>>> np.random.choice(5, 3, replace=False) # doctest: +SKIP
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array([3,1,0])
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>>> #This is equivalent to np.random.shuffle(np.arange(5))[:3]
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Generate a non-uniform random sample from np.arange(5) of size
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3 without replacement:
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>>> np.random.choice(5, 3, replace=False, p=[0.1, 0, 0.3, 0.6, 0])
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... # doctest: +SKIP
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array([2, 3, 0])
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Any of the above can be repeated with an arbitrary array-like
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instead of just integers. For instance:
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>>> aa_milne_arr = ['pooh', 'rabbit', 'piglet', 'Christopher']
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>>> np.random.choice(aa_milne_arr, 5, p=[0.5, 0.1, 0.1, 0.3])
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... # doctest: +SKIP
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array(['pooh', 'pooh', 'pooh', 'Christopher', 'piglet'],
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dtype='|S11')
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"""
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if random_state is not None:
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random_state = check_random_state(random_state)
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return random_state.choice(a, size, replace, p)
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else:
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return np.random.choice(a, size, replace, p)
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def random_choice_csc(n_samples, classes, class_probability=None,
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random_state=None):
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"""Generate a sparse random matrix given column class distributions
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Parameters
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----------
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n_samples : int,
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Number of samples to draw in each column.
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classes : list of size n_outputs of arrays of size (n_classes,)
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List of classes for each column.
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class_probability : list of size n_outputs of arrays of size (n_classes,)
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Optional (default=None). Class distribution of each column. If None the
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uniform distribution is assumed.
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random_state : int, RandomState instance or None, optional (default=None)
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If int, random_state is the seed used by the random number generator;
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If RandomState instance, random_state is the random number generator;
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If None, the random number generator is the RandomState instance used
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by `np.random`.
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Returns
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-------
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random_matrix : sparse csc matrix of size (n_samples, n_outputs)
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"""
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data = array.array('i')
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indices = array.array('i')
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indptr = array.array('i', [0])
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for j in range(len(classes)):
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classes[j] = np.asarray(classes[j])
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if classes[j].dtype.kind != 'i':
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raise ValueError("class dtype %s is not supported" %
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classes[j].dtype)
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classes[j] = classes[j].astype(np.int64, copy=False)
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# use uniform distribution if no class_probability is given
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if class_probability is None:
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class_prob_j = np.empty(shape=classes[j].shape[0])
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class_prob_j.fill(1 / classes[j].shape[0])
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else:
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class_prob_j = np.asarray(class_probability[j])
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if np.sum(class_prob_j) != 1.0:
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raise ValueError("Probability array at index {0} does not sum to "
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"one".format(j))
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if class_prob_j.shape[0] != classes[j].shape[0]:
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raise ValueError("classes[{0}] (length {1}) and "
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"class_probability[{0}] (length {2}) have "
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"different length.".format(j,
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classes[j].shape[0],
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class_prob_j.shape[0]))
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# If 0 is not present in the classes insert it with a probability 0.0
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if 0 not in classes[j]:
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classes[j] = np.insert(classes[j], 0, 0)
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class_prob_j = np.insert(class_prob_j, 0, 0.0)
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# If there are nonzero classes choose randomly using class_probability
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rng = check_random_state(random_state)
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if classes[j].shape[0] > 1:
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p_nonzero = 1 - class_prob_j[classes[j] == 0]
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nnz = int(n_samples * p_nonzero)
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ind_sample = sample_without_replacement(n_population=n_samples,
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n_samples=nnz,
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random_state=random_state)
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indices.extend(ind_sample)
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# Normalize probabilities for the nonzero elements
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classes_j_nonzero = classes[j] != 0
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class_probability_nz = class_prob_j[classes_j_nonzero]
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class_probability_nz_norm = (class_probability_nz /
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np.sum(class_probability_nz))
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classes_ind = np.searchsorted(class_probability_nz_norm.cumsum(),
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rng.rand(nnz))
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data.extend(classes[j][classes_j_nonzero][classes_ind])
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indptr.append(len(indices))
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return sp.csc_matrix((data, indices, indptr),
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(n_samples, len(classes)),
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dtype=int)
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