Document computed variable width and add a test (#4130)

* Document computed variable `width` and add a test

* Add a NEWS

Author: yutannihilation

NEWS.md

@@ -12,6 +12,8 @@
   `guides(<scale> = "none")` or `scale_*(guide = "none")` instead 
   (@yutannihilation, #4094).
 
+* `stat_bin()`'s computed variable `width` is now documented (#3522).
+
 # ggplot2 3.3.2
 This is a small release focusing on fixing regressions introduced in 3.3.1.
 

R/stat-bin.r

@@ -33,6 +33,7 @@
 #'   \item{density}{density of points in bin, scaled to integrate to 1}
 #'   \item{ncount}{count, scaled to maximum of 1}
 #'   \item{ndensity}{density, scaled to maximum of 1}
+#'   \item{width}{widths of bins}
 #' }
 #'
 #' @seealso [stat_count()], which counts the number of cases at each x

man/geom_histogram.Rd

@@ -92,6 +92,28 @@ test_that("geom_histogram() can be drawn over a 0-width range (#3043)", {
   expect_equal(out$xmax, 1.05)
 })
 
+test_that("stat_bin() provides width (#3522)", {
+  binwidth <- 1.03
+  df <- data_frame(x = 1:10)
+  p <- ggplot(df) +
+    stat_bin(
+      aes(
+        x,
+        xmin = after_stat(x - width / 2),
+        xmax = after_stat(x + width / 2),
+        ymin = after_stat(0),
+        ymax = after_stat(count)
+      ),
+      geom = "rect",
+      binwidth = binwidth
+    )
+  out <- layer_data(p)
+
+  expect_equal(nrow(out), 10)
+  # (x + width / 2) - (x - width / 2) = width
+  expect_equal(out$xmax - out$xmin, rep(binwidth, 10))
+})
+
 # Underlying binning algorithm --------------------------------------------
 
 comp_bin <- function(df, ...) {