R Multiply second dimension of 3D Array by a Vector for each of the 3rd dimension

Question

When trying to multiply the first dimension of an array by each index of a vector by the second dimension, my array is converted to a matrix and things get squirrelly. I can only do the proper multiplication long-hand.

What a mouth full...

It's easier to explain with code...

Arr <- array(runif(10*5*3), dim = c(10,5,3))
dim(Arr)
Vect <- c(1:5)

Arr[,1,1] <- Arr[,1,1]*Vect[1]
Arr[,1,2] <- Arr[,1,2]*Vect[1]
Arr[,1,3] <- Arr[,1,3]*Vect[1]

Arr[,2,1] <- Arr[,2,1]*Vect[2]
Arr[,2,2] <- Arr[,2,2]*Vect[2]
Arr[,2,3] <- Arr[,2,3]*Vect[2]

Arr[,3,1] <- Arr[,3,1]*Vect[3]
Arr[,3,2] <- Arr[,3,2]*Vect[3]
Arr[,3,3] <- Arr[,3,3]*Vect[3]

Arr[,4,1] <- Arr[,4,1]*Vect[4]
Arr[,4,2] <- Arr[,4,2]*Vect[4]
Arr[,4,3] <- Arr[,4,3]*Vect[4]

Arr[,5,1] <- Arr[,5,1]*Vect[5]
Arr[,5,2] <- Arr[,5,2]*Vect[5]
Arr[,5,3] <- Arr[,5,3]*Vect[5]

How do I clean this up to be one command?

Answer 1

Try:

sweep(Arr,2,Vect,FUN="*")

Answer 2

Cast Vect into an array first, then element multiply:

varr <- aperm(array(Vect, dim = c(5L, 10L, 3L)), perm = c(2L, 1L, 3L))

Arr <- varr * Arr

(of course we don't need to store varr if you want this in one command)

(also, turns out this is basically what sweep does under the hood...)