CODEWITHSUNDEEP
pythonlistfilterlist-comprehension
FJDU
FJDU

Reputation: 1473

Filter a list based on another list while keeping the original type

Given a list A of bool elements and another list B with the same length, the goal is to do something essentially

B = [B[i] for i in xrange(len(A)) if A[i]]

However, sometimes B is not a basic python list; for example, it might be created with manager.list(), where manager is an instance of Manager() from the multiprocessing module. The above list comprehension will turn it into a plain list, which will lose the desired function (to share data between subprocesses).

What I come up with is something like

def my_filter(A, B):
    c = 0
    for i in xrange(len(A)):
        if not A[i]:
            B.pop(i-c)
            c = c + 1

So that my_filter(A, B) will turn B into its sub-list where the elements of A are True.

However, this is a bit "ugly". Is there a more "pythonic" way to do this?

Upvotes: 0

Views: 53

Answers (1)

Joran Beasley
Joran Beasley

Reputation: 113978

maybe something like this?

B = B.__class__([itemB for itemA,itemB in zip(A,B) if itemA])

or probably better

B[:] = [itemB for itemA,itemB in zip(A,B) if itemA]

Upvotes: 1

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