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porter.py
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porter.py
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#!/usr/bin/env python
"""Porter Stemming Algorithm
This is the Porter stemming algorithm, ported to Python from the
version coded up in ANSI C by the author. It may be be regarded
as canonical, in that it follows the algorithm presented in [1]_, see also [2]_
Author - Vivake Gupta (v@nano.com), optimizations and cleanup of the code by Lars Buitinck.
Examples:
---------
>>> from gensim.parsing.porter import PorterStemmer
>>>
>>> p = PorterStemmer()
>>> p.stem("apple")
'appl'
>>>
>>> p.stem_sentence("Cats and ponies have meeting")
'cat and poni have meet'
>>>
>>> p.stem_documents(["Cats and ponies", "have meeting"])
['cat and poni', 'have meet']
.. [1] Porter, 1980, An algorithm for suffix stripping, http://www.cs.odu.edu/~jbollen/IR04/readings/readings5.pdf
.. [2] http://www.tartarus.org/~martin/PorterStemmer
"""
from six.moves import xrange
class PorterStemmer(object):
"""Class contains implementation of Porter stemming algorithm.
Attributes
--------
b : str
Buffer holding a word to be stemmed. The letters are in b[0], b[1] ... ending at b[`k`].
k : int
Readjusted downwards as the stemming progresses.
j : int
Word length.
"""
def __init__(self):
self.b = "" # buffer for word to be stemmed
self.k = 0
self.j = 0 # j is a general offset into the string
def _cons(self, i):
"""Check if b[i] is a consonant letter.
Parameters
----------
i : int
Index for `b`.
Returns
-------
bool
Examples
--------
>>> from gensim.parsing.porter import PorterStemmer
>>> p = PorterStemmer()
>>> p.b = "hi"
>>> p._cons(1)
False
>>> p.b = "meow"
>>> p._cons(3)
True
"""
ch = self.b[i]
if ch in "aeiou":
return False
if ch == 'y':
return i == 0 or not self._cons(i - 1)
return True
def _m(self):
"""Calculate the number of consonant sequences between 0 and j.
If c is a consonant sequence and v a vowel sequence, and <..>
indicates arbitrary presence,
<c><v> gives 0
<c>vc<v> gives 1
<c>vcvc<v> gives 2
<c>vcvcvc<v> gives 3
Returns
-------
int
The number of consonant sequences between 0 and j.
Examples
--------
>>> from gensim.parsing.porter import PorterStemmer
>>> p = PorterStemmer()
>>> p.b = "<bm>aobm<ao>"
>>> p.j = 11
>>> p._m()
2
"""
i = 0
while True:
if i > self.j:
return 0
if not self._cons(i):
break
i += 1
i += 1
n = 0
while True:
while True:
if i > self.j:
return n
if self._cons(i):
break
i += 1
i += 1
n += 1
while 1:
if i > self.j:
return n
if not self._cons(i):
break
i += 1
i += 1
def _vowelinstem(self):
"""Check if b[0: j + 1] contains a vowel letter.
Returns
-------
bool
Examples
--------
>>> from gensim.parsing.porter import PorterStemmer
>>> p = PorterStemmer()
>>> p.b = "gnsm"
>>> p.j = 3
>>> p._vowelinstem()
False
>>> from gensim.parsing.porter import PorterStemmer
>>> p = PorterStemmer()
>>> p.b = "gensim"
>>> p.j = 5
>>> p._vowelinstem()
True
"""
return not all(self._cons(i) for i in xrange(self.j + 1))
def _doublec(self, j):
"""Check if b[j - 1: j + 1] contain a double consonant letter.
Parameters
----------
j : int
Index for `b`
Returns
-------
bool
Examples
--------
>>> from gensim.parsing.porter import PorterStemmer
>>> p = PorterStemmer()
>>> p.b = "real"
>>> p.j = 3
>>> p._doublec(3)
False
>>> from gensim.parsing.porter import PorterStemmer
>>> p = PorterStemmer()
>>> p.b = "really"
>>> p.j = 5
>>> p._doublec(4)
True
"""
return j > 0 and self.b[j] == self.b[j - 1] and self._cons(j)
def _cvc(self, i):
"""Check if b[j - 2: j + 1] makes the (consonant, vowel, consonant) pattern and also
if the second 'c' is not 'w', 'x' or 'y'. This is used when trying to restore an 'e' at the end of a short word,
e.g. cav(e), lov(e), hop(e), crim(e), but snow, box, tray.
Parameters
----------
i : int
Index for `b`
Returns
-------
bool
Examples
--------
>>> from gensim.parsing.porter import PorterStemmer
>>> p = PorterStemmer()
>>> p.b = "lib"
>>> p.j = 2
>>> p._cvc(2)
True
>>> from gensim.parsing.porter import PorterStemmer
>>> p = PorterStemmer()
>>> p.b = "dll"
>>> p.j = 2
>>> p._cvc(2)
False
>>> from gensim.parsing.porter import PorterStemmer
>>> p = PorterStemmer()
>>> p.b = "wow"
>>> p.j = 2
>>> p._cvc(2)
False
"""
if i < 2 or not self._cons(i) or self._cons(i - 1) or not self._cons(i - 2):
return False
return self.b[i] not in "wxy"
def _ends(self, s):
"""Check if b[: k + 1] ends with `s`.
Parameters
----------
s : str
Returns
-------
bool
Examples
--------
>>> from gensim.parsing.porter import PorterStemmer
>>> p = PorterStemmer()
>>> p.b = "cowboy"
>>> p.j = 5
>>> p.k = 2
>>> p._ends("cow")
True
"""
if s[-1] != self.b[self.k]: # tiny speed-up
return False
length = len(s)
if length > (self.k + 1):
return False
if self.b[self.k - length + 1:self.k + 1] != s:
return False
self.j = self.k - length
return True
def _setto(self, s):
"""Append `s` to `b`, adjusting `k`.
Parameters
----------
s : str
"""
self.b = self.b[:self.j + 1] + s
self.k = len(self.b) - 1
def _r(self, s):
if self._m() > 0:
self._setto(s)
def _step1ab(self):
"""Get rid of plurals and -ed or -ing.
caresses -> caress
ponies -> poni
ties -> ti
caress -> caress
cats -> cat
feed -> feed
agreed -> agree
disabled -> disable
matting -> mat
mating -> mate
meeting -> meet
milling -> mill
messing -> mess
meetings -> meet
"""
if self.b[self.k] == 's':
if self._ends("sses"):
self.k -= 2
elif self._ends("ies"):
self._setto("i")
elif self.b[self.k - 1] != 's':
self.k -= 1
if self._ends("eed"):
if self._m() > 0:
self.k -= 1
elif (self._ends("ed") or self._ends("ing")) and self._vowelinstem():
self.k = self.j
if self._ends("at"):
self._setto("ate")
elif self._ends("bl"):
self._setto("ble")
elif self._ends("iz"):
self._setto("ize")
elif self._doublec(self.k):
if self.b[self.k - 1] not in "lsz":
self.k -= 1
elif self._m() == 1 and self._cvc(self.k):
self._setto("e")
def _step1c(self):
"""Turn terminal 'y' to 'i' when there is another vowel in the stem."""
if self._ends("y") and self._vowelinstem():
self.b = self.b[:self.k] + 'i'
def _step2(self):
"""Map double suffices to single ones.
So, -ization ( = -ize plus -ation) maps to -ize etc. Note that the
string before the suffix must give _m() > 0.
"""
ch = self.b[self.k - 1]
if ch == 'a':
if self._ends("ational"):
self._r("ate")
elif self._ends("tional"):
self._r("tion")
elif ch == 'c':
if self._ends("enci"):
self._r("ence")
elif self._ends("anci"):
self._r("ance")
elif ch == 'e':
if self._ends("izer"):
self._r("ize")
elif ch == 'l':
if self._ends("bli"):
self._r("ble") # --DEPARTURE--
# To match the published algorithm, replace this phrase with
# if self._ends("abli"): self._r("able")
elif self._ends("alli"):
self._r("al")
elif self._ends("entli"):
self._r("ent")
elif self._ends("eli"):
self._r("e")
elif self._ends("ousli"):
self._r("ous")
elif ch == 'o':
if self._ends("ization"):
self._r("ize")
elif self._ends("ation"):
self._r("ate")
elif self._ends("ator"):
self._r("ate")
elif ch == 's':
if self._ends("alism"):
self._r("al")
elif self._ends("iveness"):
self._r("ive")
elif self._ends("fulness"):
self._r("ful")
elif self._ends("ousness"):
self._r("ous")
elif ch == 't':
if self._ends("aliti"):
self._r("al")
elif self._ends("iviti"):
self._r("ive")
elif self._ends("biliti"):
self._r("ble")
elif ch == 'g': # --DEPARTURE--
if self._ends("logi"):
self._r("log")
# To match the published algorithm, delete this phrase
def _step3(self):
"""Deal with -ic-, -full, -ness etc. Similar strategy to _step2."""
ch = self.b[self.k]
if ch == 'e':
if self._ends("icate"):
self._r("ic")
elif self._ends("ative"):
self._r("")
elif self._ends("alize"):
self._r("al")
elif ch == 'i':
if self._ends("iciti"):
self._r("ic")
elif ch == 'l':
if self._ends("ical"):
self._r("ic")
elif self._ends("ful"):
self._r("")
elif ch == 's':
if self._ends("ness"):
self._r("")
def _step4(self):
"""Takes off -ant, -ence etc., in context <c>vcvc<v>."""
ch = self.b[self.k - 1]
if ch == 'a':
if not self._ends("al"):
return
elif ch == 'c':
if not self._ends("ance") and not self._ends("ence"):
return
elif ch == 'e':
if not self._ends("er"):
return
elif ch == 'i':
if not self._ends("ic"):
return
elif ch == 'l':
if not self._ends("able") and not self._ends("ible"):
return
elif ch == 'n':
if self._ends("ant"):
pass
elif self._ends("ement"):
pass
elif self._ends("ment"):
pass
elif self._ends("ent"):
pass
else:
return
elif ch == 'o':
if self._ends("ion") and self.b[self.j] in "st":
pass
elif self._ends("ou"):
pass
# takes care of -ous
else:
return
elif ch == 's':
if not self._ends("ism"):
return
elif ch == 't':
if not self._ends("ate") and not self._ends("iti"):
return
elif ch == 'u':
if not self._ends("ous"):
return
elif ch == 'v':
if not self._ends("ive"):
return
elif ch == 'z':
if not self._ends("ize"):
return
else:
return
if self._m() > 1:
self.k = self.j
def _step5(self):
"""Remove a final -e if _m() > 1, and change -ll to -l if m() > 1."""
k = self.j = self.k
if self.b[k] == 'e':
a = self._m()
if a > 1 or (a == 1 and not self._cvc(k - 1)):
self.k -= 1
if self.b[self.k] == 'l' and self._doublec(self.k) and self._m() > 1:
self.k -= 1
def stem(self, w):
"""Stem the word `w`.
Parameters
----------
w : str
Returns
-------
str
Stemmed version of `w`.
Examples
--------
>>> from gensim.parsing.porter import PorterStemmer
>>> p = PorterStemmer()
>>> p.stem("ponies")
'poni'
"""
w = w.lower()
k = len(w) - 1
if k <= 1:
return w # --DEPARTURE--
# With this line, strings of length 1 or 2 don't go through the
# stemming process, although no mention is made of this in the
# published algorithm. Remove the line to match the published
# algorithm.
self.b = w
self.k = k
self._step1ab()
self._step1c()
self._step2()
self._step3()
self._step4()
self._step5()
return self.b[:self.k + 1]
def stem_sentence(self, txt):
"""Stem the sentence `txt`.
Parameters
----------
txt : str
Input sentence.
Returns
-------
str
Stemmed sentence.
Examples
--------
>>> from gensim.parsing.porter import PorterStemmer
>>> p = PorterStemmer()
>>> p.stem_sentence("Wow very nice woman with apple")
'wow veri nice woman with appl'
"""
return " ".join(self.stem(x) for x in txt.split())
def stem_documents(self, docs):
"""Stem documents.
Parameters
----------
docs : list of str
Input documents
Returns
-------
list of str
Stemmed documents.
Examples
--------
>>> from gensim.parsing.porter import PorterStemmer
>>> p = PorterStemmer()
>>> p.stem_documents(["Have a very nice weekend", "Have a very nice weekend"])
['have a veri nice weekend', 'have a veri nice weekend']
"""
return [self.stem_sentence(x) for x in docs]
if __name__ == '__main__':
import sys
p = PorterStemmer()
for f in sys.argv[1:]:
with open(f) as infile:
for line in infile:
print(p.stem_sentence(line))