Python list intersection efficiency: generator or filter()?

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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

intersect python-2.7 intersection list python
4 Answers

I tried to compare the speed of 3 methods of list intersection:

import random

a = [random.randint(0, 1000) for _ in range(1000)]
b = [random.randint(0, 1000) for _ in range(1000)]

Solution 1: list comprehension

Time elapse: 8.95265507698059

import time
start = time.time()
for _ in range(1000):
    result = [x for x in a if x in b]
elapse = time.time() - start
print(elapse)

Solution 2: set

Time elapse: 0.09089064598083496

start = time.time()
for _ in range(1000):
    result = set.intersection(set(a), set(b))
elapse = time.time() - start
print(elapse)

Solution 3: numpy.intersect1d

Time elapse: 0.323300838470459

start = time.time()
for _ in range(1000):
    result = np.intersect1d(a, b)
elapse = time.time() - start
print(elapse)

Conclusion

I think use set.intersection is the fastest way.

user_70833220
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