stat_count() respects uniqueness of x (#5520)

* instead of removing, `position_stack()` sets incomplete data to missing

* adjust test

* add test

* Add news bullet

NEWS.md

@@ -1,5 +1,8 @@
 # ggplot2 (development version)
 
+* `stat_count()` treats `x` as unique in the same manner `unique()` does 
+  (#4609).
+
 * `position_stack()` no longer silently removes missing data, which is now
   handled by the geom instead of position (#3532).
 

R/stat-count.R

@@ -75,8 +75,7 @@ StatCount <- ggproto("StatCount", Stat,
     x <- data$x
     weight <- data$weight %||% rep(1, length(x))
 
-    count <- as.numeric(tapply(weight, x, sum, na.rm = TRUE))
-    count[is.na(count)] <- 0
+    count <- as.vector(rowsum(weight, x, na.rm = TRUE))
 
     bars <- data_frame0(
       count = count,

tests/testthat/test-stat-count.R

@@ -4,3 +4,14 @@ test_that("stat_count() checks the aesthetics", {
   p <- ggplot(mtcars) + stat_count(aes(factor(gear), mpg))
   expect_snapshot_error(ggplot_build(p))
 })
+
+test_that("stat_count() respects uniqueness of `x`", {
+  # For #4609, converting x to factor loses smallest digits, so here we test
+  # if they are retained
+  df <- data_frame0(x = c(1, 2, 1, 2) + rep(c(0, 1.01 * .Machine$double.eps), each = 2))
+  p <- ggplot(df, aes(x)) + stat_count(position = "identity")
+  data <- layer_data(p)
+
+  expect_length(vec_unique(df$x), 4)
+  expect_equal(data$y, rep(1, 4))
+})