Chunking sentences using the word 'but' with RegEx

问题

I am attempting to chunk sentences using RegEx at the word 'but' (or any other coordinating conjunction words). It's not working...

sentence = nltk.pos_tag(word_tokenize("There are no large collections present but there is spinal canal stenosis."))
result = nltk.RegexpParser(grammar).parse(sentence)
DigDug = nltk.RegexpParser(r'CHUNK: {.*<CC>.*}')
for subtree in DigDug.parse(sentence).subtrees(): 
    if subtree.label() == 'CHUNK': print(subtree.node())

I need to split the sentence "There are no large collections present but there is spinal canal stenosis." into two:

1. "There are no large collections present"
2. "there is spinal canal stenosis."

I also wish to use the same code to split sentences at 'and' and other coordinating conjunction (CC) words. But my code isn't working. Please help.

回答1:

I think you can simply do

import re
result = re.split(r"\s+(?:but|and)\s+", sentence)

where

`\s`        Match a single character that is a "whitespace character" (spaces, tabs, line breaks, etc.)
`+`         Between one and unlimited times, as many times as possible, giving back as needed (greedy)
`(?:`       Match the regular expression below, do not capture
            Match either the regular expression below (attempting the next alternative only if this one fails)
  `but`     Match the characters "but" literally
  `|`       Or match regular expression number 2 below (the entire group fails if this one fails to match)
  `and`     Match the characters "and" literally
)
`\s`        Match a single character that is a "whitespace character" (spaces, tabs, line breaks, etc.)
`+`         Between one and unlimited times, as many times as possible, giving back as needed (greedy)

You can add more conjunction words in there separated by a pipe-character |. Take care though that these words do not contain characters that have special meaning in regex. If in doubt, escape them first with re.escape(word)

回答2:

If you want to avoid hardcoding conjunction words like 'but' and 'and', try chinking along with chunking:

import nltk
Digdug = nltk.RegexpParser(r""" 
CHUNK_AND_CHINK:
{<.*>+}          # Chunk everything
}<CC>+{      # Chink sequences of CC
""")
sentence = nltk.pos_tag(nltk.word_tokenize("There are no large collections present but there is spinal canal stenosis."))

result = Digdug.parse(sentence)

for subtree in result.subtrees(filter=lambda t: t.label() == 
'CHUNK_AND_CHINK'):
            print (subtree)

Chinking basically excludes what we dont need from a chunk phrase - 'but' in this case. For more details , see: http://www.nltk.org/book/ch07.html

来源：https://stackoverflow.com/questions/52014482/chunking-sentences-using-the-word-but-with-regex

标签

python

regex

nltk

chunking