Allow stat_bin() to compute over single-unique-value data (#3047)

* Use the fixed binwidth when the range is 0-width

Author: yutannihilation

NEWS.md

@@ -47,6 +47,8 @@
 * `stat_bin()` will now error when the number of bins exceeds 1e6 to avoid 
   accidentally freezing the user session (@thomasp85).
 
+* `stat_bin()` now handles data with only one unique value (@yutannihilation #3047).
+
 # ggplot2 3.1.0
 
 ## Breaking changes

R/bin.R

@@ -101,6 +101,9 @@ bin_breaks_bins <- function(x_range, bins = 30, center = NULL,
   bins <- as.integer(bins)
   if (bins < 1) {
     stop("Need at least one bin.", call. = FALSE)
+  } else if (zero_range(x_range)) {
+    # 0.1 is the same width as the expansion `expand_default()` gives for 0-width data
+    width <- 0.1
   } else if (bins == 1) {
     width <- diff(x_range)
     boundary <- x_range[1]

tests/testthat/test-stat-bin.R

@@ -69,6 +69,15 @@ test_that("breaks are transformed by the scale", {
    expect_equal(out2$xmin, sqrt(c(1, 2.5)))
 })
 
+test_that("geom_histogram() can be drawn over a 0-width range (#3043)", {
+  df <- data_frame(x = rep(1, 100))
+  out <- layer_data(ggplot(df, aes(x)) + geom_histogram())
+
+  expect_equal(nrow(out), 1)
+  expect_equal(out$xmin, 0.95)
+  expect_equal(out$xmax, 1.05)
+})
+
 # Underlying binning algorithm --------------------------------------------
 
 comp_bin <- function(df, ...) {