Multiply rows of matrix by vector?
matrix, multiplication, r, vector
Solution
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.
Problem
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 ```