Swapping infinitive phrases

An infinitive phrase has the form A of B, such as book of recipes. These can often be transformed into a new form while retaining the same meaning, such as recipes book.

How to do it...

An infinitive phrase can be found by looking for a word tagged with IN. The swap_infinitive_phrase() function, defined in transforms.py, will return a chunk that swaps the portion of the phrase after the IN word with the portion before the IN word:

def swap_infinitive_phrase(chunk):
  def inpred(wt):
    word, tag = wt
    return tag == 'IN' and word != 'like'

  inidx = first_chunk_index(chunk, inpred)

  if inidx is None:
    return chunk

  nnidx = first_chunk_index(chunk, tag_startswith('NN'), start=inidx, step=-1) or 0
  return chunk[:nnidx] + chunk[inidx+1:] + chunk[nnidx:inidx]

The function can now be used to transform book of recipes into recipes book:

>>> from transforms import swap_infinitive_phrase
>>> swap_infinitive_phrase([('book', 'NN'), ('of', 'IN'...