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NLP | Swapping Verb Phrases and Noun Cardinals
  • Last Updated : 26 Feb, 2019

Need to swap verb phrases?
To eliminate the passive voice from particular phrases. This normalization is helpful with frequency analysis, by counting two apparently different phrases as the same phrase.

The code below is swap_verb_phrase class that swaps the left-hand side of the chunk with the right-hand side, using the verb as the pivot point. It uses first_chunk_index() function defined in order to find the verb to pivot around.

Code #1 : swap_verb_phrase class to swap verb

def swap_verb_phrase(chunk):
    def vbpred(wt):
        word, tag = wt
        return tag != 'VBG' and tag.startswith('VB') and len(tag) > 2
    vbidx = first_chunk_index(chunk, vbpred)
    if vbidx is None:
        return chunk
    return chunk[vbidx + 1:] + chunk[:vbidx]

Code #2 : Evaluating swap_verb_phrase

swap_verb_phrase([('the', 'DT'), ('book', 'NN'),
               ('was', 'VBD'), ('great', 'JJ')])

Output :

[('great', 'JJ'), ('the', 'DT'), ('book', 'NN')]

The code is not pivoting around a gerund because they are commonly used to describe nouns.

Code #3 :

swap_verb_phrase([('this', 'DT'), 
                  ('gripping', 'VBG'), ('book', 'NN'), 
                  ('is', 'VBZ'), ('fantastic', 'JJ')])

Output :

[('fantastic', 'JJ'), ('this', 'DT'), ('gripping', 'VBG'), ('book', 'NN')]

Swapping noun cardinals :
Cardinals in a chunk refer to a number and are tagged as CD. These cardinals occur before acardinals noun. Swapping noun cardianals is useful to put the cardinal before the noun.

Code #4 : Swapping noun cardinals

swap_noun_cardinal([('Dec.', 'NNP'), ('10', 'CD')])
swap_noun_cardinal([('the', 'DT'), ('top', 'NN'), ('10', 'CD')])

Output :

[('10', 'CD'), ('Dec.', 'NNP')]

[('the', 'DT'), ('10', 'CD'), ('top', 'NN')]


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