R/others__whichInd.R

In feng-li/flutils: Feng Li's utility functions

#' Find the raw indices for given indices in array form.
#'
#' This is exactly the inverse function of `arrayInd()'.
#' @title Raw indices finder for array.
#' @param arr.ind "matrix or vector"
#'        When it is a matrix, the length of columns should be the as the
#' length of the "dims". When it is a vector, the argument length should be
#' the same as the length of "dims".
#' @param dims "vector"
#'        The dimension of the array. Note that the last dimension is not
#' needed in the calculations,  so if you may just write "NA" there.
#' @return "vector" The raw indices.
#' @author Feng Li, Department of Statistics, Stockholm University, Sweden.
#' @note Created: Wed Mar 14 18:03:01 CET 2012;
#'       Current: Wed Mar 14 18:03:09 CET 2012.
#' @export
whichInd <- function(arr.ind, dims)
  {
    arr.indMat <- matrix(arr.ind, ncol = length(dims))
    idx1 <- cumprod(dims[-length(dims)])

    idx2 <- arr.indMat[, -1, drop = FALSE]-1
    out <- rowSums(idx1*idx2) + arr.indMat[, 1]
    return(out)
  }