345 lines
15 KiB
Python
345 lines
15 KiB
Python
# -*- coding: utf-8 -*-
|
||
#
|
||
# Natural Language Toolkit: The ISRI Arabic Stemmer
|
||
#
|
||
# Copyright (C) 2001-2018 NLTK Proejct
|
||
# Algorithm: Kazem Taghva, Rania Elkhoury, and Jeffrey Coombs (2005)
|
||
# Author: Hosam Algasaier <hosam_hme@yahoo.com>
|
||
# URL: <http://nltk.org/>
|
||
# For license information, see LICENSE.TXT
|
||
|
||
"""
|
||
ISRI Arabic Stemmer
|
||
|
||
The algorithm for this stemmer is described in:
|
||
|
||
Taghva, K., Elkoury, R., and Coombs, J. 2005. Arabic Stemming without a root dictionary.
|
||
Information Science Research Institute. University of Nevada, Las Vegas, USA.
|
||
|
||
The Information Science Research Institute’s (ISRI) Arabic stemmer shares many features
|
||
with the Khoja stemmer. However, the main difference is that ISRI stemmer does not use root
|
||
dictionary. Also, if a root is not found, ISRI stemmer returned normalized form, rather than
|
||
returning the original unmodified word.
|
||
|
||
Additional adjustments were made to improve the algorithm:
|
||
|
||
1- Adding 60 stop words.
|
||
2- Adding the pattern (تفاعيل) to ISRI pattern set.
|
||
3- The step 2 in the original algorithm was normalizing all hamza. This step is discarded because it
|
||
increases the word ambiguities and changes the original root.
|
||
|
||
"""
|
||
from __future__ import unicode_literals
|
||
import re
|
||
|
||
from nltk.stem.api import StemmerI
|
||
|
||
|
||
class ISRIStemmer(StemmerI):
|
||
'''
|
||
ISRI Arabic stemmer based on algorithm: Arabic Stemming without a root dictionary.
|
||
Information Science Research Institute. University of Nevada, Las Vegas, USA.
|
||
|
||
A few minor modifications have been made to ISRI basic algorithm.
|
||
See the source code of this module for more information.
|
||
|
||
isri.stem(token) returns Arabic root for the given token.
|
||
|
||
The ISRI Stemmer requires that all tokens have Unicode string types.
|
||
If you use Python IDLE on Arabic Windows you have to decode text first
|
||
using Arabic '1256' coding.
|
||
'''
|
||
|
||
def __init__(self):
|
||
# length three prefixes
|
||
self.p3 = ['\u0643\u0627\u0644', '\u0628\u0627\u0644',
|
||
'\u0648\u0644\u0644', '\u0648\u0627\u0644']
|
||
|
||
# length two prefixes
|
||
self.p2 = ['\u0627\u0644', '\u0644\u0644']
|
||
|
||
# length one prefixes
|
||
self.p1 = ['\u0644', '\u0628', '\u0641', '\u0633', '\u0648',
|
||
'\u064a', '\u062a', '\u0646', '\u0627']
|
||
|
||
# length three suffixes
|
||
self.s3 = ['\u062a\u0645\u0644', '\u0647\u0645\u0644',
|
||
'\u062a\u0627\u0646', '\u062a\u064a\u0646',
|
||
'\u0643\u0645\u0644']
|
||
|
||
# length two suffixes
|
||
self.s2 = ['\u0648\u0646', '\u0627\u062a', '\u0627\u0646',
|
||
'\u064a\u0646', '\u062a\u0646', '\u0643\u0645',
|
||
'\u0647\u0646', '\u0646\u0627', '\u064a\u0627',
|
||
'\u0647\u0627', '\u062a\u0645', '\u0643\u0646',
|
||
'\u0646\u064a', '\u0648\u0627', '\u0645\u0627',
|
||
'\u0647\u0645']
|
||
|
||
# length one suffixes
|
||
self.s1 = ['\u0629', '\u0647', '\u064a', '\u0643', '\u062a',
|
||
'\u0627', '\u0646']
|
||
|
||
# groups of length four patterns
|
||
self.pr4 = {0: ['\u0645'], 1: ['\u0627'],
|
||
2: ['\u0627', '\u0648', '\u064A'], 3: ['\u0629']}
|
||
|
||
# Groups of length five patterns and length three roots
|
||
self.pr53 = {0: ['\u0627', '\u062a'],
|
||
1: ['\u0627', '\u064a', '\u0648'],
|
||
2: ['\u0627', '\u062a', '\u0645'],
|
||
3: ['\u0645', '\u064a', '\u062a'],
|
||
4: ['\u0645', '\u062a'],
|
||
5: ['\u0627', '\u0648'],
|
||
6: ['\u0627', '\u0645']}
|
||
|
||
self.re_short_vowels = re.compile(r'[\u064B-\u0652]')
|
||
self.re_hamza = re.compile(r'[\u0621\u0624\u0626]')
|
||
self.re_initial_hamza = re.compile(r'^[\u0622\u0623\u0625]')
|
||
|
||
self.stop_words = ['\u064a\u0643\u0648\u0646',
|
||
'\u0648\u0644\u064a\u0633',
|
||
'\u0648\u0643\u0627\u0646',
|
||
'\u0643\u0630\u0644\u0643',
|
||
'\u0627\u0644\u062a\u064a',
|
||
'\u0648\u0628\u064a\u0646',
|
||
'\u0639\u0644\u064a\u0647\u0627',
|
||
'\u0645\u0633\u0627\u0621',
|
||
'\u0627\u0644\u0630\u064a',
|
||
'\u0648\u0643\u0627\u0646\u062a',
|
||
'\u0648\u0644\u0643\u0646',
|
||
'\u0648\u0627\u0644\u062a\u064a',
|
||
'\u062a\u0643\u0648\u0646',
|
||
'\u0627\u0644\u064a\u0648\u0645',
|
||
'\u0627\u0644\u0644\u0630\u064a\u0646',
|
||
'\u0639\u0644\u064a\u0647',
|
||
'\u0643\u0627\u0646\u062a',
|
||
'\u0644\u0630\u0644\u0643',
|
||
'\u0623\u0645\u0627\u0645',
|
||
'\u0647\u0646\u0627\u0643',
|
||
'\u0645\u0646\u0647\u0627',
|
||
'\u0645\u0627\u0632\u0627\u0644',
|
||
'\u0644\u0627\u0632\u0627\u0644',
|
||
'\u0644\u0627\u064a\u0632\u0627\u0644',
|
||
'\u0645\u0627\u064a\u0632\u0627\u0644',
|
||
'\u0627\u0635\u0628\u062d',
|
||
'\u0623\u0635\u0628\u062d',
|
||
'\u0623\u0645\u0633\u0649',
|
||
'\u0627\u0645\u0633\u0649',
|
||
'\u0623\u0636\u062d\u0649',
|
||
'\u0627\u0636\u062d\u0649',
|
||
'\u0645\u0627\u0628\u0631\u062d',
|
||
'\u0645\u0627\u0641\u062a\u0626',
|
||
'\u0645\u0627\u0627\u0646\u0641\u0643',
|
||
'\u0644\u0627\u0633\u064a\u0645\u0627',
|
||
'\u0648\u0644\u0627\u064a\u0632\u0627\u0644',
|
||
'\u0627\u0644\u062d\u0627\u0644\u064a',
|
||
'\u0627\u0644\u064a\u0647\u0627',
|
||
'\u0627\u0644\u0630\u064a\u0646',
|
||
'\u0641\u0627\u0646\u0647',
|
||
'\u0648\u0627\u0644\u0630\u064a',
|
||
'\u0648\u0647\u0630\u0627',
|
||
'\u0644\u0647\u0630\u0627',
|
||
'\u0641\u0643\u0627\u0646',
|
||
'\u0633\u062a\u0643\u0648\u0646',
|
||
'\u0627\u0644\u064a\u0647',
|
||
'\u064a\u0645\u0643\u0646',
|
||
'\u0628\u0647\u0630\u0627',
|
||
'\u0627\u0644\u0630\u0649']
|
||
|
||
def stem(self, token):
|
||
"""
|
||
Stemming a word token using the ISRI stemmer.
|
||
"""
|
||
token = self.norm(token, 1) # remove diacritics which representing Arabic short vowels
|
||
if token in self.stop_words:
|
||
return token # exclude stop words from being processed
|
||
token = self.pre32(token) # remove length three and length two prefixes in this order
|
||
token = self.suf32(token) # remove length three and length two suffixes in this order
|
||
token = self.waw(token) # remove connective ‘و’ if it precedes a word beginning with ‘و’
|
||
token = self.norm(token, 2) # normalize initial hamza to bare alif
|
||
# if 4 <= word length <= 7, then stem; otherwise, no stemming
|
||
if len(token) == 4: # length 4 word
|
||
token = self.pro_w4(token)
|
||
elif len(token) == 5: # length 5 word
|
||
token = self.pro_w53(token)
|
||
token = self.end_w5(token)
|
||
elif len(token) == 6: # length 6 word
|
||
token = self.pro_w6(token)
|
||
token = self.end_w6(token)
|
||
elif len(token) == 7: # length 7 word
|
||
token = self.suf1(token)
|
||
if len(token) == 7:
|
||
token = self.pre1(token)
|
||
if len(token) == 6:
|
||
token = self.pro_w6(token)
|
||
token = self.end_w6(token)
|
||
return token
|
||
|
||
def norm(self, word, num=3):
|
||
"""
|
||
normalization:
|
||
num=1 normalize diacritics
|
||
num=2 normalize initial hamza
|
||
num=3 both 1&2
|
||
"""
|
||
if num == 1:
|
||
word = self.re_short_vowels.sub('', word)
|
||
elif num == 2:
|
||
word = self.re_initial_hamza.sub('\u0627', word)
|
||
elif num == 3:
|
||
word = self.re_short_vowels.sub('', word)
|
||
word = self.re_initial_hamza.sub('\u0627', word)
|
||
return word
|
||
|
||
def pre32(self, word):
|
||
"""remove length three and length two prefixes in this order"""
|
||
if len(word) >= 6:
|
||
for pre3 in self.p3:
|
||
if word.startswith(pre3):
|
||
return word[3:]
|
||
if len(word) >= 5:
|
||
for pre2 in self.p2:
|
||
if word.startswith(pre2):
|
||
return word[2:]
|
||
return word
|
||
|
||
def suf32(self, word):
|
||
"""remove length three and length two suffixes in this order"""
|
||
if len(word) >= 6:
|
||
for suf3 in self.s3:
|
||
if word.endswith(suf3):
|
||
return word[:-3]
|
||
if len(word) >= 5:
|
||
for suf2 in self.s2:
|
||
if word.endswith(suf2):
|
||
return word[:-2]
|
||
return word
|
||
|
||
def waw(self, word):
|
||
"""remove connective ‘و’ if it precedes a word beginning with ‘و’ """
|
||
if len(word) >= 4 and word[:2] == '\u0648\u0648':
|
||
word = word[1:]
|
||
return word
|
||
|
||
def pro_w4(self, word):
|
||
"""process length four patterns and extract length three roots"""
|
||
if word[0] in self.pr4[0]: # مفعل
|
||
word = word[1:]
|
||
elif word[1] in self.pr4[1]: # فاعل
|
||
word = word[:1] + word[2:]
|
||
elif word[2] in self.pr4[2]: # فعال - فعول - فعيل
|
||
word = word[:2] + word[3]
|
||
elif word[3] in self.pr4[3]: # فعلة
|
||
word = word[:-1]
|
||
else:
|
||
word = self.suf1(word) # do - normalize short sufix
|
||
if len(word) == 4:
|
||
word = self.pre1(word) # do - normalize short prefix
|
||
return word
|
||
|
||
def pro_w53(self, word):
|
||
"""process length five patterns and extract length three roots"""
|
||
if word[2] in self.pr53[0] and word[0] == '\u0627': # افتعل - افاعل
|
||
word = word[1] + word[3:]
|
||
elif word[3] in self.pr53[1] and word[0] == '\u0645': # مفعول - مفعال - مفعيل
|
||
word = word[1:3] + word[4]
|
||
elif word[0] in self.pr53[2] and word[4] == '\u0629': # مفعلة - تفعلة - افعلة
|
||
word = word[1:4]
|
||
elif word[0] in self.pr53[3] and word[2] == '\u062a': # مفتعل - يفتعل - تفتعل
|
||
word = word[1] + word[3:]
|
||
elif word[0] in self.pr53[4] and word[2] == '\u0627': # مفاعل - تفاعل
|
||
word = word[1] + word[3:]
|
||
elif word[2] in self.pr53[5] and word[4] == '\u0629': # فعولة - فعالة
|
||
word = word[:2] + word[3]
|
||
elif word[0] in self.pr53[6] and word[1] == '\u0646': # انفعل - منفعل
|
||
word = word[2:]
|
||
elif word[3] == '\u0627' and word[0] == '\u0627': # افعال
|
||
word = word[1:3] + word[4]
|
||
elif word[4] == '\u0646' and word[3] == '\u0627': # فعلان
|
||
word = word[:3]
|
||
elif word[3] == '\u064a' and word[0] == '\u062a': # تفعيل
|
||
word = word[1:3] + word[4]
|
||
elif word[3] == '\u0648' and word[1] == '\u0627': # فاعول
|
||
word = word[0] + word[2] + word[4]
|
||
elif word[2] == '\u0627' and word[1] == '\u0648': # فواعل
|
||
word = word[0] + word[3:]
|
||
elif word[3] == '\u0626' and word[2] == '\u0627': # فعائل
|
||
word = word[:2] + word[4]
|
||
elif word[4] == '\u0629' and word[1] == '\u0627': # فاعلة
|
||
word = word[0] + word[2:4]
|
||
elif word[4] == '\u064a' and word[2] == '\u0627': # فعالي
|
||
word = word[:2] + word[3]
|
||
else:
|
||
word = self.suf1(word) # do - normalize short sufix
|
||
if len(word) == 5:
|
||
word = self.pre1(word) # do - normalize short prefix
|
||
return word
|
||
|
||
def pro_w54(self, word):
|
||
"""process length five patterns and extract length four roots"""
|
||
if word[0] in self.pr53[2]: # تفعلل - افعلل - مفعلل
|
||
word = word[1:]
|
||
elif word[4] == '\u0629': # فعللة
|
||
word = word[:4]
|
||
elif word[2] == '\u0627': # فعالل
|
||
word = word[:2] + word[3:]
|
||
return word
|
||
|
||
def end_w5(self, word):
|
||
"""ending step (word of length five)"""
|
||
if len(word) == 4:
|
||
word = self.pro_w4(word)
|
||
elif len(word) == 5:
|
||
word = self.pro_w54(word)
|
||
return word
|
||
|
||
def pro_w6(self, word):
|
||
"""process length six patterns and extract length three roots"""
|
||
if word.startswith('\u0627\u0633\u062a') or word.startswith('\u0645\u0633\u062a'): # مستفعل - استفعل
|
||
word = word[3:]
|
||
elif word[0] == '\u0645' and word[3] == '\u0627' and word[5] == '\u0629': # مفعالة
|
||
word = word[1:3] + word[4]
|
||
elif word[0] == '\u0627' and word[2] == '\u062a' and word[4] == '\u0627': # افتعال
|
||
word = word[1] + word[3] + word[5]
|
||
elif word[0] == '\u0627' and word[3] == '\u0648' and word[2] == word[4]: # افعوعل
|
||
word = word[1] + word[4:]
|
||
elif word[0] == '\u062a' and word[2] == '\u0627' and word[4] == '\u064a': # تفاعيل new pattern
|
||
word = word[1] + word[3] + word[5]
|
||
else:
|
||
word = self.suf1(word) # do - normalize short sufix
|
||
if len(word) == 6:
|
||
word = self.pre1(word) # do - normalize short prefix
|
||
return word
|
||
|
||
def pro_w64(self, word):
|
||
"""process length six patterns and extract length four roots"""
|
||
if word[0] == '\u0627' and word[4] == '\u0627': # افعلال
|
||
word = word[1:4] + word[5]
|
||
elif word.startswith('\u0645\u062a'): # متفعلل
|
||
word = word[2:]
|
||
return word
|
||
|
||
def end_w6(self, word):
|
||
"""ending step (word of length six)"""
|
||
if len(word) == 5:
|
||
word = self.pro_w53(word)
|
||
word = self.end_w5(word)
|
||
elif len(word) == 6:
|
||
word = self.pro_w64(word)
|
||
return word
|
||
|
||
def suf1(self, word):
|
||
"""normalize short sufix"""
|
||
for sf1 in self.s1:
|
||
if word.endswith(sf1):
|
||
return word[:-1]
|
||
return word
|
||
|
||
def pre1(self, word):
|
||
"""normalize short prefix"""
|
||
for sp1 in self.p1:
|
||
if word.startswith(sp1):
|
||
return word[1:]
|
||
return word
|
||
|
||
|