Select along one of n dimensions in array

Question

I have an array in R, created by a function like this:

A <- array(data=NA, dim=c(2,4,4), dimnames=list(c(\"x\",\"y\"),NULL,NULL))

And I

Answer 1

I wrote this general function. Not necessarily super fast but a nice application for arrayInd and matrix indexing:

extract <- function(A, .dim, .value) {

    val.idx  <- match(.value, dimnames(A)[[.dim]])
    all.idx  <- arrayInd(seq_along(A), dim(A))
    keep.idx <- all.idx[all.idx[, .dim] == val.idx, , drop = FALSE]
    array(A[keep.idx], dim = dim(A)[-.dim], dimnames = dimnames(A)[-.dim])

}

Example:

A <- array(data=1:32, dim=c(2,4,4),
           dimnames=list(c("x","y"), LETTERS[1:4], letters[1:4]))

extract(A, 1, "x")
extract(A, 2, "D")
extract(A, 3, "b")