Replace values in df/matrix based on another matrix/df in R

Question

I have two data frames, one contains numbers, and the second is binary, both are the same size. I would now like to replace all numbers in data frame A with NA if the corresponding variable in data frame B is 0 and not 1. If it is 1 the number should remain unchanged. How do I go about that?

df A

   A  B  C
1  34 32 12
2  52 23 34

df B

   A  B  C
1  1  1  1
2  0  0  1

desired result

   A  B  C
1  34 32 12
2  na na 34

Answer 1

If you're working with matrices, it's as simple as mat1[which(mat2 == 0)] <- NA.

Answer 2

I found my answer, after reading the docs I thought the replace command worked only for vectors, but the following does the trick:

new.df <- replace(A.df, B.df == 0, "NaN")