Python filter over a function with two arguments?

Question

What I'm trying to do is take a list and filter it based on comparisons of adjacent list members. Namely, something like this

filter(lambda x,y: x != y, someList)

to get rid of duplicate elements right next to each other. I can easily implement this other ways, but started out trying to do it with a list reduction/filter and am stubborn enough to want to keep trying until I figure it out. I am still not that experienced in python, but I feel like there is something like this that I am missing.

Thanks!

What other ways have you considered? It'd help if you post those (and is someList actually a list or sequence or some arbitrary iterable) etc... (desired input and output samples would also be good) — Jon Clements
– Jon Clements, Commented Feb 22, 2013 at 5:15

johnsyweb · Accepted Answer · 2013-02-22 05:19:27Z

4

def unique_justseen(iterable, key=None):
    "List unique elements, preserving order. Remember only the element just seen."
    # unique_justseen('AAAABBBCCDAABBB') --> A B C D A B
    # unique_justseen('ABBCcAD', str.lower) --> A B C A D
    return imap(next, imap(itemgetter(1), groupby(iterable, key)))

Source: Python Documentation, 9.7.2. Recipes.

There's a wealth of great stuff in itertools for efficient looping.

answered Feb 22, 2013 at 5:19

johnsyweb

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Jon Clements · Accepted Answer · 2013-02-22 05:20:57Z

3

For consecutive elements (duplicate elements) then:

>>> from itertools import groupby
>>> items = 'aaaabbdeeeeefg'
>>> ''.join(k for k, g in groupby(items))
'abdefg'

answered Feb 22, 2013 at 5:20

Jon Clements

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