Default bar width calculated panel-wise (#5125)

* `geom_bar()` uses panelwise resolution

* Add test

* Add NEWS bullet

Author: teunbrand

NEWS.md

@@ -1,5 +1,7 @@
 # ggplot2 (development version)
 
+* The default width of `geom_bar()` is now based on panel-wise resolution of
+  the data, rather than global resolution (@teunbrand, #4336).
 * To apply dodging more consistently in violin plots, `stat_ydensity()` now
   has a `drop` argument to keep or discard groups with 1 observation.
 * Aesthetics listed in `geom_*()` and `stat_*()` layers now point to relevant

R/geom-bar.R

@@ -144,7 +144,10 @@ GeomBar <- ggproto("GeomBar", GeomRect,
     data$flipped_aes <- params$flipped_aes
     data <- flip_data(data, params$flipped_aes)
     data$width <- data$width %||%
-      params$width %||% (resolution(data$x, FALSE) * 0.9)
+      params$width %||% (min(vapply(
+        split(data$x, data$PANEL),
+        resolution, numeric(1), zero = FALSE
+      )) * 0.9)
     data$just <- params$just %||% 0.5
     data <- transform(data,
       ymin = pmin(y, 0), ymax = pmax(y, 0),

tests/testthat/test-geom-bar.R

@@ -24,3 +24,27 @@ test_that("geom_bar works in both directions", {
   y$flipped_aes <- NULL
   expect_identical(x, flip_data(y, TRUE))
 })
+
+test_that("geom_bar default widths considers panels", {
+
+  dat <- data_frame0(x = c(1:2, 1:2 + 0.1), y = 1,
+                    PANEL = factor(rep(1:2, each = 2)))
+
+  layer  <- geom_bar()
+  params <- layer$geom_params
+
+  # Default should be panel-wise resolution (0.9), not data-wise resolution (0.1)
+  new <- layer$geom$setup_data(dat, params)
+  expect_equal(
+    new$xmax - new$xmin,
+    rep(0.9, 4)
+  )
+
+  # Check that default can still be overridden
+  params$width <- 0.5
+  new <- layer$geom$setup_data(dat, params)
+  expect_equal(
+    new$xmax - new$xmin,
+    rep(0.5, 4)
+  )
+})