elfuego1 elfuego1 - 6 months ago 27
Python Question

Python - Intersection of two lists

I know how to get an intersection of two flat lists:

b1 = [1,2,3,4,5,9,11,15]
b2 = [4,5,6,7,8]
b3 = [val for val in b1 if val in b2]


or

def intersect(a, b):
return list(set(a) & set(b))

print intersect(b1, b2)


But when I have to find intersection for nested lists then my problems starts:

c1 = [1, 6, 7, 10, 13, 28, 32, 41, 58, 63]
c2 = [[13, 17, 18, 21, 32], [7, 11, 13, 14, 28], [1, 5, 6, 8, 15, 16]]


In the end I would like to receive:

c3 = [[13,32],[7,13,28],[1,6]]


Can you guys give me a hand with this?

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Answer

If you want:

c1 = [1, 6, 7, 10, 13, 28, 32, 41, 58, 63]
c2 = [[13, 17, 18, 21, 32], [7, 11, 13, 14, 28], [1, 5, 6, 8, 15, 16]]
c3 = [[13, 32], [7, 13, 28], [1,6]]

Then here is your solution for Python 2:

c3 = [filter(lambda x: x in c1, sublist) for sublist in c2]

In Python 3 filter returns an iterable instead of list, so you need to wrap filter calls with list():

c3 = [list(filter(lambda x: x in c1, sublist)) for sublist in c2]

Explanation:

The filter part takes each sublist's item and checks to see if it is in the source list c1. The list comprehension is executed for each sublist in c2.

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