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

Perhaps there is an easier way, but this works:

do.call("[",c(list(A,"x"),lapply(dim(A)[-1],seq)))
     [,1] [,2] [,3] [,4]
[1,]   NA   NA   NA   NA
[2,]   NA   NA   NA   NA
[3,]   NA   NA   NA   NA
[4,]   NA   NA   NA   NA

Let's generalize it into a function that can extract from any dimension, not necessarily the first one:

extract <- function(A, .dim, .value) {
    idx.list <- lapply(dim(A), seq_len)
    idx.list[[.dim]] <- .value
    do.call(`[`, c(list(A), idx.list))
}

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")