Insert Nan into specific positions in a vector

Question

I have two vectors called A and B: A is a list of numbers and B is a list that indicates the order that the numbers of A should be arranged.

I would like to create a vector C, where the numbers of vector A are arranged according to the positions laid out in vector B.

The numbers in A don't cover the entire range of possible positions in B, so I need to create a vector C with NaN or [] for missing A values. What is the fastest way of doing this?

See example below:

A = [5, 10, 55, 3, 10]
B = [1, 3, 4, 6, 9]
C = [5, nan, 10, 55, nan, 3, nan, nan, 10]

Thanks for your help!

Answer 1

try

C = [A[B.index(i)] if i in B else nan for i in range(max(B) + 1)]
# [nan, 5, nan, 10, 55, nan, 3, nan, nan, 10]

or if you really want to skip index 0:

C = [A[B.index(i)] if i in B else nan for i in range(1, max(B) + 1)]
# [5, nan, 10, 55, nan, 3, nan, nan, 10]