R: How can I fix my for-loop so it multiplies every element of a row with the corresponding element of a column?

Question

I have a matrix beta with nrow=10 and ncol=10 and a second matrix data with nrow=10 and ncol=10 . I want to multiply the columns from beta with the rows from data for ever element.

I already tried to write a for loop:

solution1 <- matrix(NA,10,10)

for(i in 1:nrow(data)){solution <- matrix(beta*data[i,])}

but this jut shows me a list of 10 times "NA"

I don't know what I am doing wrong. I actually expect a matrix with nrow=10 and ncol=10 . Maybe someone has an idea and can help?

Answer 1

The operation of multiplying each element of a row of a matrix with the corresponding element of a column of another matrix is the same as the matrix multiplication defined in linear algebra.

R has a matrix multiplication operator %*%

solution <- beta %*% data

After reading your clarification I found the following simple solution. Multiplying all values element-wise and then taking the transpose of the matrix.

solution <- t(beta*data)

Which outputs the following results

     [,1] [,2] [,3]
[1,]    1    4    9
[2,]   16   25   36
[3,]   49   64   81