Question

I have two matrices

A
2 1 0
0 1 6
1 0 0
B 
1 1 3
4 2 8
2 0 1

I want to find out the elements comparing A and B satisfying the following criteria:

if A[i,j] =0 and B[i,j]>0

So my result matrix should be

C
0 0 3
4 0 0
0 0 1

What is a proper way to do this except for a for loop?

Answer 1

Regular logical and arithmetic operators act element wise on matrices in R. Only the %*% and kronecker operators do matrix multiplication. Furthermore you can index matrixes using the “[” and “[<-” functions:

> C <- B
> C[!( A==0 & B >0) ] <- 0
> C
     [,1] [,2] [,3]
[1,]    0    0    3
[2,]    4    0    0
[3,]    0    0    1