How to match two arrays

Question

I have two arrays

A = [a, b, c, d]

and

B = [a1, a2, b1, b2, b3, c1, c2, c3, d1, d2, d3, d4]

I want to match b

Answer 1

In pretty Python:

di = {}
for item in A:
    di[item] = filter(lambda v: v.startswith(item), B)