I am trying to use (s)apply to multiply two matrices with different dimensions. The matrices are:
xx <- matrix(c(1, 2, 3, 4, 5, 6), nrow=2, ncol=3, byrow=T)
yy <- matrix(c(10, 100), nrow=2, ncol=1, byrow=T)
What I want is to multiply each row of one matrix for each row of the other matrix and obtain this:
> zz
[,1] [,2] [,3]
[1,] 10 20 30
[2,] 400 500 600
I have tried sapply(yy, function(x) xx*x) which produces a 6x2 matrix instead of the 3x2 matrix I want. Also apply(yy, 2, function(x) xx*x) which produces a 6x1 matrix does not work.
In a similar situation in the past I used sapply without problem so I do not understand why this is not working now (I always had a bit of trouble in wrapping my head around *apply). What am I doing wrong?
Convert yy to a vector by c() and it will be recycled to the dimension of xx when multiplying.
xx * c(yy)
# [,1] [,2] [,3]
# [1,] 10 20 30
# [2,] 400 500 600
Or by matrix multiplication :
diag(c(yy)) %*% xx