Python - Chunk Classification

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Classification based chunking involves classifying the text as a group of words rather than individual words. A simple scenario is tagging the text in sentences. We will use a corpus to demonstrate the classification. We choose the corpus conll2000 which has data from the of the Wall Street Journal corpus (WSJ) used for noun phrase-based chunking.

First, we add the corpus to our environment using the following command.

import nltk
nltk.download('conll2000')

Lets have a look at the first few sentences in this corpus. 

from nltk.corpus import conll2000

x = (conll2000.sents())
for i in range(3):
     print x[i]
     print '\n'

When we run the above program we get the following output −


['Confidence', 'in', 'the', 'pond', 'is', 'widely', 'expected', 'to', 'take', 'another', 'sharp', 'dive', 'if', 'trade', 'figres', 'for', 'September', ',', 'de', 'for', 'release', 'tomorrow', ',', 'fail', 'to', 'show', 'a', 'sbstantial', 'improvement', 'from', 'Jly', 'and', 'Agst', "'s", 'near-record', 'deficits', '.']


['Chancellor', 'of', 'the', 'Excheqer', 'Nigel', 'Lawson', "'s", 'restated', 'commitment', 'to', 'a', 'firm', 'monetary', 'policy', 'has', 'helped', 'to', 'prevent', 'a', 'freefall', 'in', 'sterling', 'over', 'the', 'past', 'week', '.']


['Bt', 'analysts', 'reckon', 'nderlying', 'spport', 'for', 'sterling', 'has', 'been', 'eroded', 'by', 'the', 'chancellor', "'s", 'failre', 'to', 'annonce', 'any', 'new', 'policy', 'measres', 'in', 'his', 'Mansion', 'Hose', 'speech', 'last', 'Thrsday', '.']

Next we use the fucntion tagged_sents() to get the sentences tagged to their classifiers. 

from nltk.corpus import conll2000

x = (conll2000.tagged_sents())
for i in range(3):
     print x[i]
     print '\n'

When we run the above program we get the following output −

[('Confidence', 'NN'), ('in', 'IN'), ('the', 'DT'), ('pond', 'NN'), ('is', 'VBZ'), ('widely', 'RB'), ('expected', 'VBN'), ('to', 'TO'), ('take', 'VB'), ('another', 'DT'), ('sharp', 'JJ'), ('dive', 'NN'), ('if', 'IN'), ('trade', 'NN'), ('figres', 'NNS'), ('for', 'IN'), ('September', 'NNP'), (',', ','), ('de', 'JJ'), ('for', 'IN'), ('release', 'NN'), ('tomorrow', 'NN'), (',', ','), ('fail', 'VB'), ('to', 'TO'), ('show', 'VB'), ('a', 'DT'), ('sbstantial', 'JJ'), ('improvement', 'NN'), ('from', 'IN'), ('Jly', 'NNP'), ('and', 'CC'), ('Agst', 'NNP'), ("'s", 'POS'), ('near-record', 'JJ'), ('deficits', 'NNS'), ('.', '.')]


[('Chancellor', 'NNP'), ('of', 'IN'), ('the', 'DT'), ('Excheqer', 'NNP'), ('Nigel', 'NNP'), ('Lawson', 'NNP'), ("'s", 'POS'), ('restated', 'VBN'), ('commitment', 'NN'), ('to', 'TO'), ('a', 'DT'), ('firm', 'NN'), ('monetary', 'JJ'), ('policy', 'NN'), ('has', 'VBZ'), ('helped', 'VBN'), ('to', 'TO'), ('prevent', 'VB'), ('a', 'DT'), ('freefall', 'NN'), ('in', 'IN'), ('sterling', 'NN'), ('over', 'IN'), ('the', 'DT'), ('past', 'JJ'), ('week', 'NN'), ('.', '.')]


[('Bt', 'CC'), ('analysts', 'NNS'), ('reckon', 'VBP'), ('nderlying', 'VBG'), ('spport', 'NN'), ('for', 'IN'), ('sterling', 'NN'), ('has', 'VBZ'), ('been', 'VBN'), ('eroded', 'VBN'), ('by', 'IN'), ('the', 'DT'), ('chancellor', 'NN'), ("'s", 'POS'), ('failre', 'NN'), ('to', 'TO'), ('annonce', 'VB'), ('any', 'DT'), ('new', 'JJ'), ('policy', 'NN'), ('measres', 'NNS'), ('in', 'IN'), ('his', 'PRP$'), ('Mansion', 'NNP'), ('Hose', 'NNP'), ('speech', 'NN'), ('last', 'JJ'), ('Thrsday', 'NNP'), ('.', '.')]
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