Multiply rows of matrix by vector?

Question

I have a numeric matrix with 25 columns and 23 rows, and a vector of length 25. How can I multiply each row of the matrix by the vector without using a for loop?

The result should be a 25x23 matrix (the same size as the input), but each row has been multiplied by the vector.

Added reproducible example from @hatmatrix's answer:

matrix <- matrix(rep(1:3,each=5),nrow=3,ncol=5,byrow=TRUE)       [,1] [,2] [,3] [,4] [,5] [1,]    1    1    1    1    1 [2,]    2    2    2    2    2 [3,]    3    3    3    3    3  vector <- 1:5 

Desired output:

     [,1] [,2] [,3] [,4] [,5] [1,]    1    2    3    4    5 [2,]    2    4    6    8   10 [3,]    3    6    9   12   15 

Answer 1

I think you're looking for sweep().

# Create example data and vector mat <- matrix(rep(1:3,each=5),nrow=3,ncol=5,byrow=TRUE)      [,1] [,2] [,3] [,4] [,5] [1,]    1    1    1    1    1 [2,]    2    2    2    2    2 [3,]    3    3    3    3    3  vec <- 1:5  # Use sweep to apply the vector with the multiply (`*`) function #  across columns (See ?apply for an explanation of MARGIN)  sweep(mat, MARGIN=2, vec, `*`)      [,1] [,2] [,3] [,4] [,5] [1,]    1    2    3    4    5 [2,]    2    4    6    8   10 [3,]    3    6    9   12   15 

It's been one of R's core functions, though improvements have been made on it over the years.