95 lines
2.5 KiB
R
95 lines
2.5 KiB
R
#' Matricization
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#'
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#' @param T multi-dimensional array
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#' @param modes axis indices along to matricize
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#' @param dims dimension of \code{T} befor matricization
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#' @param inv boolean to determin if the inverse operation should be performed
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#'
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#' @returns matrix of dimensions \code{dims[modes]} by \code{prod(dims)[-modes]}
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#' or tensor of dimensions \code{dims} iff \code{inv} is true.
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#'
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#' @examples
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#' A <- array(rnorm(2 * 3 * 5), dim = c(2, 3, 5))
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#' stopifnot(exprs = {
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#' all.equal(A, mat(mat(A, 1), 1, dim(A), TRUE))
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#' all.equal(A, mat(mat(A, 2), 2, dim(A), TRUE))
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#' all.equal(A, mat(mat(A, 3), 3, dim(A), TRUE))
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#' all.equal(A, mat(mat(A, c(1, 2)), c(1, 2), dim(A), TRUE))
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#' all.equal(A, mat(mat(A, c(1, 3)), c(1, 3), dim(A), TRUE))
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#' all.equal(A, mat(mat(A, c(2, 3)), c(2, 3), dim(A), TRUE))
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#'
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#' all.equal(t(mat(A, 1)), mat(A, c(2, 3)))
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#' all.equal(t(mat(A, 3)), mat(A, c(1, 2)))
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#' })
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#'
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#' stopifnot(all.equal(
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#' mat(1:12, 2, dims = c(2, 3, 2)),
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#' matrix(c(
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#' 1, 2, 7, 8,
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#' 3, 4, 9, 10,
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#' 5, 6, 11, 12
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#' ), 3, 4, byrow = TRUE)
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#' ))
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#'
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#' @export
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mat <- function(T, modes, dims = dim(T), inv = FALSE) {
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modes <- as.integer(modes)
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stopifnot(exprs = {
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length(T) == prod(dims)
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all(modes <= length(dims))
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})
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perm <- c(modes, seq_along(dims)[-modes])
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if (inv) {
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dim(T) <- dims[perm]
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perm <- order(perm)
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} else {
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dim(T) <- dims
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}
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T <- aperm(T, perm)
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if (inv) {
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dim(T) <- dims
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} else {
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dim(T) <- c(prod(dims[modes]), prod(dims[-modes]))
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}
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T
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}
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# #' Inverse Matricization
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# #'
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# #' @param T matrix of dimensions \code{dims[mode]} by \code{prod(dims[-mode])}
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# #' @param mode axis along the original matricization
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# #' @param dims dimension of the original tensor
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# #'
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# #' @returns multi-dimensional array of dimensions \code{dims}
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# #'
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# #' @examples
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# #' p <- c(2, 3, 5)
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# #' A <- array(rnorm(prod(p)), dim = p)
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# #' stopifnot(expr = {
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# #' all.equal(A, mat.inv(mat(A, 1), 1, p))
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# #' all.equal(A, mat.inv(mat(A, 2), 2, p))
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# #' all.equal(A, mat.inv(mat(A, 3), 3, p))
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# #' })
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# #'
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# #' @export
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# mat.inv <- function(T, modes, dims) {
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# modes <- as.integer(modes)
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# stopifnot(exprs = {
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# length(T) == prod(dims)
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# any(length(dims) < modes)
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# })
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# dim(T) <- c(dims[modes], dims[-modes])
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# T <- aperm(T, order(c(modes, seq_along(dims)[-modes])))
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# dim(T) <- c(prod(dims[modes]), prod(dims[-modes]))
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# T
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# }
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