The function aperm(a, perm) may be used to permute an array, a.
The argument perm must be a permutation of the integers 
1,
2, ..., k
, where k is the number of subscripts in a.
The result of the function is an array of the same size as a but with
old dimension given by perm[j] becoming the new jth dimension.
The easiest way to think of this operation is as a generalization of
transposition for matrices. Indeed if A is a matrix, (i.e. a doubly
subscripted array) then B given by
B <- aperm(A, c(2,1))
is just the transpose of A. For this special case a simpler function t() is available, so we could have used B <- t(A).