#' Create your own discrete scale
#'
#' This allows you to specify you own set of mappings from levels in the
#' data to aesthetic values.
#'
#' @inheritParams scale_x_discrete
#' @param values a set of aesthetic values to map data values to. If this
#' is a named vector, then the values will be matched based on the names.
#' If unnamed, values will be matched in order (usually alphabetical) with
#' the limits of the scale. Any data values that don't match will be
#' given \code{na.value}.
#' @examples
#' p <- ggplot(mtcars, aes(mpg, wt)) +
#' geom_point(aes(colour = factor(cyl)))
#' p + scale_colour_manual(values = c("red", "blue", "green"))
#'
#' # It's recommended to use a named vector
#' cols <- c("8" = "red", "4" = "blue", "6" = "darkgreen", "10" = "orange")
#' p + scale_colour_manual(values = cols)
#'
#' # As with other scales you can use breaks to control the appearance
#' # of the legend.
#' p + scale_colour_manual(values = cols)
#' p + scale_colour_manual(
#' values = cols,
#' breaks = c("4", "6", "8"),
#' labels = c("four", "six", "eight")
#' )
#'
#' # And limits to control the possible values of the scale
#' p + scale_colour_manual(values = cols, limits = c("4", "8"))
#' p + scale_colour_manual(values = cols, limits = c("4", "6", "8", "10"))
#' @name scale_manual
#' @aliases NULL
NULL
#' @rdname scale_manual
#' @export
scale_colour_manual <- function(..., values) {
manual_scale("colour", values, ...)
}
#' @rdname scale_manual
#' @export
scale_fill_manual <- function(..., values) {
manual_scale("fill", values, ...)
}
#' @rdname scale_manual
#' @export
scale_size_manual <- function(..., values) {
manual_scale("size", values, ...)
}
#' @rdname scale_manual
#' @export
scale_shape_manual <- function(..., values) {
manual_scale("shape", values, ...)
}
#' @rdname scale_manual
#' @export
scale_linetype_manual <- function(..., values) {
manual_scale("linetype", values, ...)
}
#' @rdname scale_manual
#' @export
scale_alpha_manual <- function(..., values) {
manual_scale("alpha", values, ...)
}
manual_scale <- function(aesthetic, values, ...) {
pal <- function(n) {
if (n > length(values)) {
stop("Insufficient values in manual scale. ", n, " needed but only ",
length(values), " provided.", call. = FALSE)
}
values
}
discrete_scale(aesthetic, "manual", pal, ...)
}
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