Intersection of the lists in a list (list of lists) in python

Question

I have a list of lists, like follow:

list = [[1,2,3],[2,3,4],[3,4,5],[3,5,6]]

I want to find the intersection of them in python 2.7, I mean

intersect_list = [3]

Thanks.

@cricket_007 I tried pairwise intersection between a result and every element of list, but I think it is not an optimal way, should I write it here? — user137927, Dec 09 '16 at 19:58

kdopen · Accepted Answer · 2016-12-09T19:58:23.970

12

First, don't use list as a variable name - it hides the built in class.

Next, this will do it

>>> a = [[1,2,3],[2,3,4],[3,4,5],[3,5,6]]
>>> set.intersection(*map(set,a))
{3}

The map(set,a) simply converts it to a list of sets. Then you just unpack the list and find the intersection.

If you really need the result as a list, just wrap the call with list(...)

edited Dec 09 '16 at 19:58

answered Dec 09 '16 at 19:56

kdopen

https://docs.python.org/2/library/stdtypes.html#set.intersection – Stats4224 Dec 09 '16 at 19:57
You could use `set(a[0]).intersection(*a[1:])` which would avoid needing to convert most of the lists to sets. – Dan D. Dec 09 '16 at 20:00
You could do `set(m[0]).intersection(*m[1:])` for refusing of converting all the sublists to `set`. – Mazdak Dec 09 '16 at 20:00
Nifty use of the unpacking: https://www.python.org/dev/peps/pep-3132/ – Stats4224 Dec 09 '16 at 20:00
Yeah, but I just prefer the straightforward call to map. Seems cleaner and more intuitive. You need to understand unpacking either way – kdopen Dec 09 '16 at 20:05
@DanD. Oh! Thanks. – user137927 Dec 09 '16 at 20:11
@Kasramvd Thanks you too – user137927 Dec 09 '16 at 20:11

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