R/Cdiff.R

In RegSDC: Information Preserving Regression-Based Tools for Statistical Disclosure Control

#' Matrix difference (a-b) including checking for equal columns
#' 
#' Each column is checked by \code{\link{all.equal}}
#'
#' @param a numerical matrix
#' @param b numerical matrix
#' @param tolerance parameter to \code{\link{all.equal}}
#'
#' @return (a-b) where equal columns are set to zero
#' @keywords internal
#' @export
#'
#' @examples
#' a <- matrix(rnorm(6), 3, 2)
#' b <- matrix(rnorm(6), 3, 2)
#' a - b
#' Cdiff(a, b)
#' b[, 1] <- a[, 1] + (.Machine$double.eps)^(2/3) * b[, 1]
#' a - b
#' Cdiff(a, b)
#' a[, 2] <- b[, 2]
#' a - b
#' Cdiff(a, b)
Cdiff <- function(a, b, tolerance = sqrt(.Machine$double.eps)) {
  d <- a - b
  n <- ncol(d)
  equalCol <- rep(FALSE, n)
  for (i in seq_len(n)) {
    equalCol[i] <- isTRUE(all.equal(a[, i], b[, i], tolerance = tolerance))
  }
  d[, equalCol] <- 0
  d
}