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#
# Natural Language Toolkit: ARLSTem Stemmer
#
# Copyright (C) 2001-2023 NLTK Project
#
# Author: Kheireddine Abainia (x-programer) <[email protected]>
# Algorithms: Kheireddine Abainia <[email protected]>
# Siham Ouamour
# Halim Sayoud
# URL: <https://www.nltk.org/>
# For license information, see LICENSE.TXT
"""
ARLSTem Arabic Stemmer
The details about the implementation of this algorithm are described in:
K. Abainia, S. Ouamour and H. Sayoud, A Novel Robust Arabic Light Stemmer ,
Journal of Experimental & Theoretical Artificial Intelligence (JETAI'17),
Vol. 29, No. 3, 2017, pp. 557-573.
The ARLSTem is a light Arabic stemmer that is based on removing the affixes
from the word (i.e. prefixes, suffixes and infixes). It was evaluated and
compared to several other stemmers using Paice's parameters (under-stemming
index, over-stemming index and stemming weight), and the results showed that
ARLSTem is promising and producing high performances. This stemmer is not
based on any dictionary and can be used on-line effectively.
"""
import re
from nltk.stem.api import StemmerI
class ARLSTem(StemmerI):
"""
ARLSTem stemmer : a light Arabic Stemming algorithm without any dictionary.
Department of Telecommunication & Information Processing. USTHB University,
Algiers, Algeria.
ARLSTem.stem(token) returns the Arabic stem for the input token.
The ARLSTem Stemmer requires that all tokens are encoded using Unicode
encoding.
"""
def __init__(self):
# different Alif with hamza
self.re_hamzated_alif = re.compile(r"[\u0622\u0623\u0625]")
self.re_alifMaqsura = re.compile(r"[\u0649]")
self.re_diacritics = re.compile(r"[\u064B-\u065F]")
# Alif Laam, Laam Laam, Fa Laam, Fa Ba
self.pr2 = ["\u0627\u0644", "\u0644\u0644", "\u0641\u0644", "\u0641\u0628"]
# Ba Alif Laam, Kaaf Alif Laam, Waaw Alif Laam
self.pr3 = ["\u0628\u0627\u0644", "\u0643\u0627\u0644", "\u0648\u0627\u0644"]
# Fa Laam Laam, Waaw Laam Laam
self.pr32 = ["\u0641\u0644\u0644", "\u0648\u0644\u0644"]
# Fa Ba Alif Laam, Waaw Ba Alif Laam, Fa Kaaf Alif Laam
self.pr4 = [
"\u0641\u0628\u0627\u0644",
"\u0648\u0628\u0627\u0644",
"\u0641\u0643\u0627\u0644",
]
# Kaf Yaa, Kaf Miim
self.su2 = ["\u0643\u064A", "\u0643\u0645"]
# Ha Alif, Ha Miim
self.su22 = ["\u0647\u0627", "\u0647\u0645"]
# Kaf Miim Alif, Kaf Noon Shadda
self.su3 = ["\u0643\u0645\u0627", "\u0643\u0646\u0651"]
# Ha Miim Alif, Ha Noon Shadda
self.su32 = ["\u0647\u0645\u0627", "\u0647\u0646\u0651"]
# Alif Noon, Ya Noon, Waaw Noon
self.pl_si2 = ["\u0627\u0646", "\u064A\u0646", "\u0648\u0646"]
# Taa Alif Noon, Taa Ya Noon
self.pl_si3 = ["\u062A\u0627\u0646", "\u062A\u064A\u0646"]
# Alif Noon, Waaw Noon
self.verb_su2 = ["\u0627\u0646", "\u0648\u0646"]
# Siin Taa, Siin Yaa
self.verb_pr2 = ["\u0633\u062A", "\u0633\u064A"]
# Siin Alif, Siin Noon
self.verb_pr22 = ["\u0633\u0627", "\u0633\u0646"]
# Lam Noon, Lam Taa, Lam Yaa, Lam Hamza
self.verb_pr33 = [
"\u0644\u0646",
"\u0644\u062A",
"\u0644\u064A",
"\u0644\u0623",
]
# Taa Miim Alif, Taa Noon Shadda
self.verb_suf3 = ["\u062A\u0645\u0627", "\u062A\u0646\u0651"]
# Noon Alif, Taa Miim, Taa Alif, Waaw Alif
self.verb_suf2 = [
"\u0646\u0627",
"\u062A\u0645",
"\u062A\u0627",
"\u0648\u0627",
]
# Taa, Alif, Noon
self.verb_suf1 = ["\u062A", "\u0627", "\u0646"]
def stem(self, token):
"""
call this function to get the word's stem based on ARLSTem .
"""
try:
if token is None:
raise ValueError(
"The word could not be stemmed, because \
it is empty !"
)
# remove Arabic diacritics and replace some letters with others
token = self.norm(token)
# strip common prefixes of the nouns
pre = self.pref(token)
if pre is not None:
token = pre
# strip the suffixes which are common to nouns and verbs
token = self.suff(token)
# transform a plural noun to a singular noun
ps = self.plur2sing(token)
if ps is None:
# transform from the feminine form to the masculine form
fm = self.fem2masc(token)
if fm is not None:
return fm
else:
if pre is None: # if the prefixes are not stripped
# strip the verb prefixes and suffixes
return self.verb(token)
else:
return ps
return token
except ValueError as e:
print(e)
def norm(self, token):
"""
normalize the word by removing diacritics, replacing hamzated Alif
with Alif replacing AlifMaqsura with Yaa and removing Waaw at the
beginning.
"""
# strip Arabic diacritics
token = self.re_diacritics.sub("", token)
# replace Hamzated Alif with Alif bare
token = self.re_hamzated_alif.sub("\u0627", token)
# replace alifMaqsura with Yaa
token = self.re_alifMaqsura.sub("\u064A", token)
# strip the Waaw from the word beginning if the remaining is 3 letters
# at least
if token.startswith("\u0648") and len(token) > 3:
token = token[1:]
return token
def pref(self, token):
"""
remove prefixes from the words' beginning.
"""
if len(token) > 5:
for p3 in self.pr3:
if token.startswith(p3):
return token[3:]
if len(token) > 6:
for p4 in self.pr4:
if token.startswith(p4):
return token[4:]
if len(token) > 5:
for p3 in self.pr32:
if token.startswith(p3):
return token[3:]
if len(token) > 4:
for p2 in self.pr2:
if token.startswith(p2):
return token[2:]
def suff(self, token):
"""
remove suffixes from the word's end.
"""
if token.endswith("\u0643") and len(token) > 3:
return token[:-1]
if len(token) > 4:
for s2 in self.su2:
if token.endswith(s2):
return token[:-2]
if len(token) > 5:
for s3 in self.su3:
if token.endswith(s3):
return token[:-3]
if token.endswith("\u0647") and len(token) > 3:
token = token[:-1]
return token
if len(token) > 4:
for s2 in self.su22:
if token.endswith(s2):
return token[:-2]
if len(token) > 5:
for s3 in self.su32:
if token.endswith(s3):
return token[:-3]
if token.endswith("\u0646\u0627") and len(token) > 4:
return token[:-2]
return token
def fem2masc(self, token):
"""
transform the word from the feminine form to the masculine form.
"""
if token.endswith("\u0629") and len(token) > 3:
return token[:-1]
def plur2sing(self, token):
"""
transform the word from the plural form to the singular form.
"""
if len(token) > 4:
for ps2 in self.pl_si2:
if token.endswith(ps2):
return token[:-2]
if len(token) > 5:
for ps3 in self.pl_si3:
if token.endswith(ps3):
return token[:-3]
if len(token) > 3 and token.endswith("\u0627\u062A"):
return token[:-2]
if len(token) > 3 and token.startswith("\u0627") and token[2] == "\u0627":
return token[:2] + token[3:]
if len(token) > 4 and token.startswith("\u0627") and token[-2] == "\u0627":
return token[1:-2] + token[-1]
def verb(self, token):
"""
stem the verb prefixes and suffixes or both
"""
vb = self.verb_t1(token)
if vb is not None:
return vb
vb = self.verb_t2(token)
if vb is not None:
return vb
vb = self.verb_t3(token)
if vb is not None:
return vb
vb = self.verb_t4(token)
if vb is not None:
return vb
vb = self.verb_t5(token)
if vb is not None:
return vb
return self.verb_t6(token)
def verb_t1(self, token):
"""
stem the present prefixes and suffixes
"""
if len(token) > 5 and token.startswith("\u062A"): # Taa
for s2 in self.pl_si2:
if token.endswith(s2):
return token[1:-2]
if len(token) > 5 and token.startswith("\u064A"): # Yaa
for s2 in self.verb_su2:
if token.endswith(s2):
return token[1:-2]
if len(token) > 4 and token.startswith("\u0627"): # Alif
# Waaw Alif
if len(token) > 5 and token.endswith("\u0648\u0627"):
return token[1:-2]
# Yaa
if token.endswith("\u064A"):
return token[1:-1]
# Alif
if token.endswith("\u0627"):
return token[1:-1]
# Noon
if token.endswith("\u0646"):
return token[1:-1]
# ^Yaa, Noon$
if len(token) > 4 and token.startswith("\u064A") and token.endswith("\u0646"):
return token[1:-1]
# ^Taa, Noon$
if len(token) > 4 and token.startswith("\u062A") and token.endswith("\u0646"):
return token[1:-1]
def verb_t2(self, token):
"""
stem the future prefixes and suffixes
"""
if len(token) > 6:
for s2 in self.pl_si2:
# ^Siin Taa
if token.startswith(self.verb_pr2[0]) and token.endswith(s2):
return token[2:-2]
# ^Siin Yaa, Alif Noon$
if token.startswith(self.verb_pr2[1]) and token.endswith(self.pl_si2[0]):
return token[2:-2]
# ^Siin Yaa, Waaw Noon$
if token.startswith(self.verb_pr2[1]) and token.endswith(self.pl_si2[2]):
return token[2:-2]
# ^Siin Taa, Noon$
if (
len(token) > 5
and token.startswith(self.verb_pr2[0])
and token.endswith("\u0646")
):
return token[2:-1]
# ^Siin Yaa, Noon$
if (
len(token) > 5
and token.startswith(self.verb_pr2[1])
and token.endswith("\u0646")
):
return token[2:-1]
def verb_t3(self, token):
"""
stem the present suffixes
"""
if len(token) > 5:
for su3 in self.verb_suf3:
if token.endswith(su3):
return token[:-3]
if len(token) > 4:
for su2 in self.verb_suf2:
if token.endswith(su2):
return token[:-2]
if len(token) > 3:
for su1 in self.verb_suf1:
if token.endswith(su1):
return token[:-1]
def verb_t4(self, token):
"""
stem the present prefixes
"""
if len(token) > 3:
for pr1 in self.verb_suf1:
if token.startswith(pr1):
return token[1:]
if token.startswith("\u064A"):
return token[1:]
def verb_t5(self, token):
"""
stem the future prefixes
"""
if len(token) > 4:
for pr2 in self.verb_pr22:
if token.startswith(pr2):
return token[2:]
for pr2 in self.verb_pr2:
if token.startswith(pr2):
return token[2:]
return token
def verb_t6(self, token):
"""
stem the order prefixes
"""
if len(token) > 4:
for pr3 in self.verb_pr33:
if token.startswith(pr3):
return token[2:]
return token
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