Add value matching to breaks in manual_scale

NEWS.md

@@ -84,6 +84,12 @@
 
 * Increase the default `nbin` of `guide_colourbar()` to place the ticks more precisely (#3508, @yutannihilation).
 
+* Modified `manual_scale` to match `values` with the order of `breaks` whenever
+  `values` is an unnamed vector. Previously, unnamed `values` would be matched
+  to the limits of the scale and ignore the order of any `breaks` provided. Note
+  that this may change the appearance of plots that previously relied on the
+  unordered behaviour. (#2429, @idno0001)
+
 # ggplot2 3.2.1
 
 This is a patch release fixing a few regressions introduced in 3.2.0 as well as

R/scale-manual.r

@@ -17,11 +17,11 @@
 #'   name(s) of the aesthetic(s) that this scale works with. This can be useful, for
 #'   example, to apply colour settings to the `colour` and `fill` aesthetics at the
 #'   same time, via `aesthetics = c("colour", "fill")`.
-#' @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 `na.value`.
+#' @param values a set of aesthetic values to map data values to. The values
+#'   will be matched in order (usually alphabetical) with the limits of the
+#'   scale, or with `breaks` if provided. If this is a named vector, then the
+#'   values will be matched based on the names instead. Data values that don't
+#'   match will be given `na.value`.
 #' @section Color Blindness:
 #' Many color palettes derived from RGB combinations (like the "rainbow" color
 #' palette) are not suitable to support all viewers, especially those with
@@ -124,6 +124,18 @@ manual_scale <- function(aesthetic, values = NULL, ...) {
     force(values)
   }
 
+  # order values according to breaks
+  args <- list(...)
+  if (is.vector(values) && is.null(names(values))
+      && "breaks" %in% names(args)) {
+    if (length(args[["breaks"]]) != length(values)) {
+      stop("Differing number of values and breaks in manual scale. ",
+           length(values), " values provided compared to ",
+           length(args[["breaks"]]), " breaks.", call. = FALSE)
+    }
+    names(values) <- args[["breaks"]]
+  }
+
   pal <- function(n) {
     if (n > length(values)) {
       stop("Insufficient values in manual scale. ", n, " needed but only ",

tests/testthat/test-scale-manual.r

@@ -67,3 +67,17 @@ test_that("generic scale can be used in place of aesthetic-specific scales", {
 
   expect_equal(layer_data(p1), layer_data(p2))
 })
+
+test_that("named values do not match with breaks in manual scales", {
+   s <- scale_fill_manual(values = c("data_red" = "red", "data_black" = "black"),
+                          breaks = c("data_black", "data_red"))
+   s$train(c("data_black", "data_red"))
+   expect_equal(s$map(c("data_red", "data_black")), c("red", "black"))
+})
+
+test_that("unnamed values match breaks in manual scales", {
+   s <- scale_fill_manual(values = c("red", "black"),
+                          breaks = c("data_red", "data_black"))
+   s$train(c("data_red", "data_black"))
+   expect_equal(s$map(c("data_red", "data_black")), c("red", "black"))
+})