Element-wise boolean multiplication

Question

I'm looking for the most beautiful and short way to multiply those types of lists:

a = [True, False, True, False, False]

b = [100, 200]

Length of b equals to number of True elements in a

The answer that I need is [100, 0, 200, 0, 0] here

Are there any simple ways to get that answer?
It looks like element-wise multiplication, but the fact is that the size of the second list is smaller, so common numpy methods don't work without bad code.

Hope, you'll find nice solution

Answer 1

You could do this in numpy:

c = np.array(a).astype(int)

c[c==1] = b

>>> c
array([100,   0, 200,   0,   0])

Note If you need the result as a list (based on your desired output), rather than a numpy array, use c.tolist()

Answer 2

There's a pretty clean iterator based solution

it = iter(b)
[next(it) if x else 0 for x in a]
# [100, 0, 200, 0, 0]