Take the intersection of an arbitrary number of lists in python

Question

Suppose I have a list of lists of elements which are all the same (i'll use ints in this example)

[range(100)[::4], range(100)[::3], range(100)[::2], range(100)[::1]]

What would be a nice and/or efficient way to take the intersection of these lists (so you would get every element that is in each of the lists)? For the example that would be:

[0, 12, 24, 36, 48, 60, 72, 84, 96]

Answer 1

Use sets, which have an intersection method.

>>> s = set()
>>> s.add(4)
>>> s.add(5)
>>> s
set([4, 5])
>>> t = set([2, 4, 9])
>>> s.intersection(t)
set([4])

For your example, something like

>>> data = [range(100)[::4], range(100)[::3], range(100)[::2], range(100)[::1]]
>>> sets = map(set, data)
>>> print set.intersection(*sets)
set([0, 96, 36, 72, 12, 48, 84, 24, 60])

Answer 2

I think the built-in set module should do the trick.

>>> elements = [range(100)[::4], range(100)[::3], range(100)[::2], range(100)[::1]]
>>> sets = map(set, elements)
>>> result = list(reduce(lambda x, y: x & y, sets))
>>> print result
[0, 96, 36, 72, 12, 48, 84, 24, 60]