Python maintain order in intersection of lists

Question

I have a list A and list B, I want to get common elements from the two lists but want when I get the common elements they should maintain the order of List A.

First I started with converting them in to set and taking the intersection but that had the problem of maintaining the order.

common = list(set(A).intersection(set(B)))

so I decided to do list comprehension:

common = [i for i in A if i in B]

I am getting

IndexError: too many indices for array

Answer 1

As a general answer for such problems You can use sorted function with lambda x:A.index(x) as its key that will sort the result based on the order of list A:

>>> common = sorted(set(A).intersection(B) ,key=lambda x:A.index(x))

Also Note that you don't need use set(B) for intersection.

Answer 2

Your code (common = [i for i in A if i in B]) works just fine. Perhaps what you wrote in your question was not the exact code that raised the IndexError.

You can speedup membership tests by making a set from B:

set_b = set(B)
common = [i for i in A if i in set_b]