--- a
+++ b/R/unscale.R
@@ -0,0 +1,42 @@
+#' Unscales a scaled data.frame
+#'
+#' \code{unscale} is a generic function that unscale and/or uncenter the columns
+#' of a matrix generated by the scale base function
+#'
+#' @param x A numeric matrix.
+#'
+#' @return
+#' Return a matrix, uncenterd and unscaled. Attributes "scaled:center" and
+#' "scaled:scale" are removed.
+#'
+#'
+#' @details
+#' \code{unscale} uses attributes added by the scale function "scaled:scale" and
+#' "scaled:center" and use these scaling factor to retrieve the initial matrix.
+#' It first unscales and then uncenters.
+#'
+#'
+#' @seealso \code{\link[base]{scale}}
+#'
+#' @examples
+#' X <- matrix(1:9, ncol = 3)
+#' X.scale <- scale(X, center = TRUE, scale = TRUE)
+#' X.unscale <- unscale(X.scale)
+#' all(X == X.unscale)
+#'
+#' @export
+unscale <- function(x){
+    stopifnot(is(x, "matrix"))
+    attrib <- attributes(x)
+
+    if("scaled:scale" %in% names(attrib)){
+        x  <- x * attrib$`scaled:scale`
+        attr(x, "scaled:scale") <- NULL
+    }
+    if("scaled:center" %in% names(attrib)){
+        x <- x + matrix(rep(attrib$`scaled:center`,
+                            each = nrow(x)), nrow = nrow(x))
+        attr(x, "scaled:center") <- NULL
+    }
+    return(x)
+}