#' 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)
}