If I have an array A
A <- array(0, c(4, 3, 5))
for(i in 1:5) {
set.seed(i)
A[, , i] <- matrix(rnorm(12), 4, 3)
}
and if I have matrix B
set.seed(6)
B <- matrix(rnorm(12), 4, 3)
The code to subtract B from the each matrix of the array A would be:
d<-array(0, c(4,3,5))
for(i in 1:5){
d[,,i]<-A[,,i]-B
}
However, what would be the code to perform the same calculation using a function from "apply" family?
This is what sweep
is for.
sweep(A, 1:2, B)
Maybe not very intuitive:
A[] <- apply(A, 3, `-`, B)
Because you are looping on the last array dimension, you can simply do:
d <- A - as.vector(B)
and it will be much faster. It is the same idea as when you subtract a vector from a matrix: the vector is recycled so it is subtracted to each column.
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