Python list intersection efficiency: generator or filter()?

python list intersection python-2.7 intersect
Amnon Grossman picture Amnon Grossman · Jun 16, 2011 · Viewed 10.7k times · Source

I would like to intersect two lists in Python (2.7). I need the result to be iterable:

list1 = [1,2,3,4]
list2 = [3,4,5,6]
result = (3,4) # any kind of iterable

Providing a full iteration will be performed first thing after the intersection, which of the following is more efficient?

Using a generator:

result = (x for x in list1 if x in list2)

Using filter():

result = filter(lambda x: x in list2, list1)

Other suggestions?

Thanks in advance,
Amnon

Answer

Daniel Roseman picture Daniel Roseman · Jun 16, 2011

Neither of these. The best way is to use sets.

list1 = [1,2,3,4]
list2 = [3,4,5,6]
result = set(list1).intersection(list2)

Sets are iterable, so no need to convert the result into anything.

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