Is there a way to remove duplicate and continuous words/phrases in a string?

Question

Is there a way to remove duplicate and continuous words/phrases in a string? E.g.

[in]: foo foo bar bar foo bar

Answer 1

I love itertools. It seems like every time I want to write something, itertools already has it. In this case, groupby takes a list and groups repeated, sequential items from that list into a tuple of (item_value, iterator_of_those_values). Use it here like:

>>> s = 'this is a foo bar bar black sheep , have you any any wool woo , yes sir yes sir three bag woo wu wool'
>>> ' '.join(item[0] for item in groupby(s.split()))
'this is a foo bar black sheep , have you any wool woo , yes sir yes sir three bag woo wu wool'

So let's extend that a little with a function that returns a list with its duplicated repeated values removed:

from itertools import chain, groupby

def dedupe(lst):
    return list(chain(*[item[0] for item in groupby(lst)]))

That's great for one-word phrases, but not helpful for longer phrases. What to do? Well, first, we'll want to check for longer phrases by striding over our original phrase:

def stride(lst, offset, length):
    if offset:
        yield lst[:offset]

    while True:
        yield lst[offset:offset + length]
        offset += length
        if offset >= len(lst):
            return

Now we're cooking! OK. So our strategy here is to first remove all the single-word duplicates. Next, we'll remove the two-word duplicates, starting from offset 0 then 1. After that, three-word duplicates starting at offsets 0, 1, and 2, and so on until we've hit five-word duplicates:

def cleanse(list_of_words, max_phrase_length):
    for length in range(1, max_phrase_length + 1):
        for offset in range(length):
            list_of_words = dedupe(stride(list_of_words, offset, length))

    return list_of_words

Putting it all together:

from itertools import chain, groupby

def stride(lst, offset, length):
    if offset:
        yield lst[:offset]

    while True:
        yield lst[offset:offset + length]
        offset += length
        if offset >= len(lst):
            return

def dedupe(lst):
    return list(chain(*[item[0] for item in groupby(lst)]))

def cleanse(list_of_words, max_phrase_length):
    for length in range(1, max_phrase_length + 1):
        for offset in range(length):
            list_of_words = dedupe(stride(list_of_words, offset, length))

    return list_of_words

a = 'this is a sentence sentence sentence this is a sentence where phrases phrases duplicate where phrases duplicate . sentence are not prhases .'

b = 'this is a sentence where phrases duplicate . sentence are not prhases .'

print ' '.join(cleanse(a.split(), 5)) == b