Hi guys,

assume I have two matrices, and I want to get the third, C. If value of the first column of A is the same to a value of the first column in B, when this condition is TRUE I want to add to a final C the third column of A

A = matrix(  c(5, 0, 0,3, 1, 5, 7,3,4),  nrow=3, ncol=3) 
B = matrix(  c(2, 0, 0,3, 1, 5, 7,3,4,0,2,1),  nrow=4, ncol=2) 

> A
     [,1] [,2] [,3]
[1,]    5    3    7
[2,]    0    1    3
[3,]    0    5    4
> B
     [,1] [,2]
[1,]    2    1
[2,]    0    5
[3,]    0    7
[4,]    3    3

output C:
0   5  3
0   7  4

I managed to extract those which are equal, but I don't know how to add the third column of A.

s=B[B[,1]%in%A[,1],]
s
     [,1] [,2]
[1,]    0    5
[2,]    0    7

I tried apply(), my output is following. Not sure why I get 1 and 1?

> a=cbind(s, apply(s, 2, function(z) any(A[,1] %in% B[,1])))
> a
     [,1] [,2] [,3]
[1,]    0    5    1
[2,]    0    7    1

thank you,