Python - 词干提取算法

在自然语言处理领域，我们遇到过两个或多个词有共同词根的情况。 例如，agreed、agreeing 和 agreeable这三个词具有相同的词根 agree。 涉及这些词中的任何一个的搜索应将它们视为同一个词，即根词。 因此，将所有单词链接到它们的词根变得至关重要。 NLTK 库具有执行此链接并提供显示词根的输出的方法。

nltk 中提供了三种最常用的词干提取算法。 他们给出的结果略有不同。 下面的示例显示了所有三种词干提取算法的使用及其结果。

import nltk
from nltk.stem.porter import PorterStemmer
from nltk.stem.lancaster import LancasterStemmer
from nltk.stem import SnowballStemmer 

porter_stemmer = PorterStemmer()
lanca_stemmer = LancasterStemmer()
sb_stemmer = SnowballStemmer("english",)

word_data = "Aging head of famous crime family decides to transfer his position to one of his subalterns" 
# First Word tokenization
nltk_tokens = nltk.word_tokenize(word_data)
#Next find the roots of the word
print '***PorterStemmer****\n'
for w_port in nltk_tokens:
   print "Actual: %s  || Stem: %s"  % (w_port,porter_stemmer.stem(w_port))

print '\n***LancasterStemmer****\n'    
for w_lanca in nltk_tokens:
      print "Actual: %s  || Stem: %s"  % (w_lanca,lanca_stemmer.stem(w_lanca))
print '\n***SnowballStemmer****\n' 

for w_snow in nltk_tokens:
      print "Actual: %s  || Stem: %s"  % (w_snow,sb_stemmer.stem(w_snow))   

当我们运行上面的程序时，得到以下输出 −

***PorterStemmer****

Actual: Aging  || Stem: age
Actual: head  || Stem: head
Actual: of  || Stem: of
Actual: famous  || Stem: famou
Actual: crime  || Stem: crime
Actual: family  || Stem: famili
Actual: decides  || Stem: decid
Actual: to  || Stem: to
Actual: transfer  || Stem: transfer
Actual: his  || Stem: hi
Actual: position  || Stem: posit
Actual: to  || Stem: to
Actual: one  || Stem: one
Actual: of  || Stem: of
Actual: his  || Stem: hi
Actual: subalterns  || Stem: subaltern

***LancasterStemmer****

Actual: Aging  || Stem: ag
Actual: head  || Stem: head
Actual: of  || Stem: of
Actual: famous  || Stem: fam
Actual: crime  || Stem: crim
Actual: family  || Stem: famy
Actual: decides  || Stem: decid
Actual: to  || Stem: to
Actual: transfer  || Stem: transf
Actual: his  || Stem: his
Actual: position  || Stem: posit
Actual: to  || Stem: to
Actual: one  || Stem: on
Actual: of  || Stem: of
Actual: his  || Stem: his
Actual: subalterns  || Stem: subaltern

***SnowballStemmer****

Actual: Aging  || Stem: age
Actual: head  || Stem: head
Actual: of  || Stem: of
Actual: famous  || Stem: famous
Actual: crime  || Stem: crime
Actual: family  || Stem: famili
Actual: decides  || Stem: decid
Actual: to  || Stem: to
Actual: transfer  || Stem: transfer
Actual: his  || Stem: his
Actual: position  || Stem: posit
Actual: to  || Stem: to
Actual: one  || Stem: one
Actual: of  || Stem: of
Actual: his  || Stem: his
Actual: subalterns  || Stem: subaltern