R/map_values.R

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#' Replace specified values with new values, in a vector or factor (from plyr)
#'
#' Item in x that match items from will be replaced by items in to, matched by position. For example, items in x that match the first element in from will be replaced by the first element of to.
#'
#' @param x the factor or vector to modify
#' @param from a vector of the items to replace
#' @param to a vector of replacement values
#' @param warn_missing print a message if any of the old values are not actually present in x
#'
#' @details  If x is a factor, the matching levels of the factor will be replaced with the new values.
#' The related revalue function works only on character vectors and factors, but this function works on vectors of any type and factors.
#'
#' @examples
#' x <- c("a", "b", "c")
#'map_values(x, c("a", "c"), c("A", "C"))
#'
#'# Works on factors
#'y <- factor(c("a", "b", "c", "a"))
#'map_values(y, c("a", "c"), c("A", "C"))
#'
#'# Works on numeric vectors
#'z <- c(1, 4, 5, 9)
#'map_values(z, from = c(1, 5, 9), to = c(10, 50, 90))
#'
#' @export

map_values <- function (x, from, to, warn_missing = TRUE)
{
  if (length(from) != length(to)) {
    stop("`from` and `to` vectors are not the same length.")
  }
  if (!is.atomic(x)) {
    stop("`x` must be an atomic vector.")
  }
  if (is.factor(x)) {
    levels(x) <- map_values(levels(x), from, to, warn_missing)
    return(x)
  }
  mapidx <- match(x, from)
  mapidxNA <- is.na(mapidx)
  from_found <- sort(unique(mapidx))
  if (warn_missing && length(from_found) != length(from)) {
    message("The following `from` values were not present in `x`: ",
            paste(from[!(1:length(from) %in% from_found)], collapse = ", "))
  }
  x[!mapidxNA] <- to[mapidx[!mapidxNA]]
  x
}