Mid-point color is now the middle of the diverging color scale (#3086)

* Fixed color number in scale_color_distiller() and scale_fill_distiller()

* add unit test

* add news bullet. closes #3072

* changed name format

Author: dariyasydykova

NEWS.md

@@ -23,6 +23,8 @@
 * Default labels are now generated more consistently; e.g., symbols no longer
   get backticks, and long expressions are abbreviated with `...`
   (@yutannihilation, #2981).
+  
+* Diverging brewer color scale now has the correct mid-point color (@dariyasydykova, #3072).
 
 * Aesthetic mappings now accept functions that return `NULL` (@yutannihilation,
   #2997).

R/scale-brewer.r

@@ -8,7 +8,7 @@
 #'
 #' @note
 #' The `distiller` scales extend brewer to continuous scales by smoothly
-#' interpolating 6 colours from any palette to a continuous scale.
+#' interpolating 7 colours from any palette to a continuous scale.
 #'
 #' @details
 #' The `brewer` scales were carefully designed and tested on discrete data.
@@ -84,8 +84,9 @@ scale_colour_distiller <- function(..., type = "seq", palette = 1, direction = -
     warning("Using a discrete colour palette in a continuous scale.\n  Consider using type = \"seq\" or type = \"div\" instead", call. = FALSE)
   }
   continuous_scale(aesthetics, "distiller",
-    gradient_n_pal(brewer_pal(type, palette, direction)(6), values, space), na.value = na.value, guide = guide, ...)
-  # NB: 6 colours per palette gives nice gradients; more results in more saturated colours which do not look as good
+    gradient_n_pal(brewer_pal(type, palette, direction)(7), values, space), na.value = na.value, guide = guide, ...)
+  # NB: 6-7 colours per palette gives nice gradients; more results in more saturated colours which do not look as good
+  # For diverging scales, you need an odd number to make sure the mid-point is in the center
 }
 
 #' @export
@@ -96,7 +97,7 @@ scale_fill_distiller <- function(..., type = "seq", palette = 1, direction = -1,
     warning("Using a discrete colour palette in a continuous scale.\n  Consider using type = \"seq\" or type = \"div\" instead", call. = FALSE)
   }
   continuous_scale(aesthetics, "distiller",
-    gradient_n_pal(brewer_pal(type, palette, direction)(6), values, space), na.value = na.value, guide = guide, ...)
+    gradient_n_pal(brewer_pal(type, palette, direction)(7), values, space), na.value = na.value, guide = guide, ...)
 }
 
 # icon.brewer <- function() {

man/scale_brewer.Rd

@@ -0,0 +1,17 @@
+context("scale_brewer")
+
+test_that("mid-point in diverging brewer color scale", {
+  d <- data_frame(x = -1:1)
+
+  p <- ggplot(d) +
+    aes(x = x, y = 1, color = x) +
+    scale_color_distiller(palette = 'RdBu', direction = 1, limits = c(-1, 1))
+
+  expect_equal(layer_data(p)$colour, c("#B2182B", "#F7F7F7", "#2166AC"))
+
+  p <- ggplot(d) +
+    aes(x = x, y = 1, fill = x) +
+    scale_fill_distiller(palette = 'RdBu', direction = 1, limits = c(-1, 1))
+
+  expect_equal(layer_data(p)$fill, c("#B2182B", "#F7F7F7", "#2166AC"))
+})