Drop space for unused limits in scale_discrete

Fixes #1638 

* Use get_limit in call to dimension

NEWS.md

@@ -87,6 +87,14 @@
 
 * A warning is now issued when a scale transformation introduces infinite 
   values in a scale (#1696)
+
+* Fixed bug where space for dropped levels in scale_discrete would be preserved 
+  (#1638)
+
+* Fixed bug where scale expansion was not used correctly for discrete scales
+
+* ggplot2 now warns when breaks are dropped due to using continuous data on a 
+  discrete scale (#1589)
 
 * Quantile lines in geom_violin() are no longer affected by the alpha aesthetic
   (@mnbram, #1714)

R/scale-discrete-.r

@@ -73,7 +73,6 @@ scale_y_discrete <- function(..., expand = waiver()) {
 #' @usage NULL
 #' @export
 ScaleDiscretePosition <- ggproto("ScaleDiscretePosition", ScaleDiscrete,
-
   train = function(self, x) {
     if (is.discrete(x)) {
       self$range$train(x, drop = self$drop)
@@ -84,6 +83,7 @@ ScaleDiscretePosition <- ggproto("ScaleDiscretePosition", ScaleDiscrete,
 
   get_limits = function(self) {
     if (self$is_empty()) return(c(0, 1))
+
     self$limits %||% self$range$range %||% integer()
   },
 
@@ -106,14 +106,14 @@ ScaleDiscretePosition <- ggproto("ScaleDiscretePosition", ScaleDiscrete,
 
   dimension = function(self, expand = c(0, 0)) {
     c_range <- self$range_c$range
-    d_range <- self$range$range
+    d_range <- self$get_limits()
 
     if (self$is_empty()) {
       c(0, 1)
-    } else if (is.null(d_range)) { # only continuous
-      expand_range(c_range, expand[1], 0 , 1)
+    } else if (is.null(self$range$range)) { # only continuous
+      expand_range(c_range, expand[1], expand[2] , 1)
     } else if (is.null(c_range)) { # only discrete
-      expand_range(c(1, length(d_range)), 0, expand[2], 1)
+      expand_range(c(1, length(d_range)), expand[1], expand[2], 1)
     } else { # both
       range(
         expand_range(c_range, expand[1], 0 , 1),
@@ -122,6 +122,10 @@ ScaleDiscretePosition <- ggproto("ScaleDiscretePosition", ScaleDiscrete,
     }
   },
 
+  get_breaks = function(self, limits = self$get_limits()) {
+    ggproto_parent(ScaleDiscrete, self)$get_breaks(limits)
+  },
+
   clone = function(self) {
     new <- ggproto(NULL, self)
     new$range <- discrete_range()

tests/testthat/test-scale-discrete.R

@@ -16,3 +16,10 @@ test_that("discrete ranges also encompas continuous values", {
   expect_equal(x_range(base + geom_point(aes(x1)) + geom_point(aes(x2))), c(0, 4))
 })
 
+test_that("discrete scale shrinks to range when setting limits", {
+  df <- data.frame(x = letters[1:10], y = 1:10)
+  p <- ggplot(df, aes(x, y)) + geom_point() +
+    scale_x_discrete(limits = c("a", "b"))
+
+  expect_equal(layer_scales(p)$x$dimension(c(0, 1)), c(0, 3))
+})