Don't reorder data during faceting. (#2694)

* Don't change data order in facet_grid() or facet_wrap(). Enables data vectors to be provided
via aes() or as parameters.

* add news item

Author: clauswilke

NEWS.md

@@ -1,8 +1,13 @@
 # ggplot2 3.0.0.9000
 
-* `geom_hex()` now understands the `size` and `linetype` aesthetics
-  (@mikmart, #2488).
+*  `geom_hex()` now understands the `size` and `linetype` aesthetics
+   (@mikmart, #2488).
 
+*   Data is no longer internally reordered when faceting. This makes it safer to
+    feed data columns into `aes()` or into parameters of geoms or stats. However,
+    doing so remains discouraged (@clauswilke).
+
+
 # ggplot2 3.0.0
 
 ## Breaking changes

R/facet-grid-.r

@@ -288,7 +288,7 @@ FacetGrid <- ggproto("FacetGrid", Facet,
 
       data$PANEL <- layout$PANEL[match(keys$x, keys$y)]
     }
-    data[order(data$PANEL), , drop = FALSE]
+    data
   },
   draw_panels = function(panels, layout, x_scales, y_scales, ranges, coord, data, theme, params) {
     if ((params$free$x || params$free$y) && !coord$is_free()) {

R/facet-wrap.r

@@ -199,7 +199,7 @@ FacetWrap <- ggproto("FacetWrap", Facet,
     keys <- plyr::join.keys(facet_vals, layout, by = names(vars))
 
     data$PANEL <- layout$PANEL[match(keys$x, keys$y)]
-    data[order(data$PANEL), ]
+    data
   },
   draw_panels = function(panels, layout, x_scales, y_scales, ranges, coord, data, theme, params) {
     if ((params$free$x || params$free$y) && !coord$is_free()) {

tests/testthat/test-facet-map.r

@@ -31,7 +31,7 @@ test_that("grid: missing facet columns are duplicated", {
 
   loc_a <- panel_map_one(facet, df_a, plot_data = df)
   expect_equal(nrow(loc_a), 4)
-  expect_equal(loc_a$PANEL, factor(1:4))
+  expect_equal(loc_a$PANEL, factor(c(1, 3, 2, 4)))
 
   loc_b <- panel_map_one(facet, df_b, plot_data = df)
   expect_equal(nrow(loc_b), 4)
@@ -47,8 +47,8 @@ test_that("wrap: missing facet columns are duplicated", {
 
   loc_a <- panel_map_one(facet, df_a, plot_data = df)
   expect_equal(nrow(loc_a), 4)
-  expect_equal(loc_a$PANEL, factor(1:4))
-  expect_equal(loc_a$a, c(1, 1, 2, 2))
+  expect_equal(loc_a$PANEL, factor(c(1, 3, 2, 4)))
+  expect_equal(loc_a$a, c(1, 2, 1, 2))
 
   loc_b <- panel_map_one(facet, df_b, plot_data = df)
   expect_equal(nrow(loc_b), 4)