Apply jitter in position_jitterdodge() once (#5819)

* Follow #4403

* add test

* add news bullet

Author: teunbrand

NEWS.md

@@ -79,6 +79,8 @@
   returns input unaltered (@teunbrand, #5800).
 * `width` is implemented as aesthetic instead of parameter in `geom_col()` and
   `geom_bar()` (#3142).
+* Fix a bug in `position_jitterdodge()` where different jitters would be applied
+  to different position aesthetics of the same axis (@teunbrand, #5818).
 
 # ggplot2 3.5.1
 

R/position-jitterdodge.R

@@ -76,7 +76,18 @@ PositionJitterdodge <- ggproto("PositionJitterdodge", Position,
     trans_x <- if (params$jitter.width > 0) function(x) jitter(x, amount = params$jitter.width)
     trans_y <- if (params$jitter.height > 0) function(x) jitter(x, amount = params$jitter.height)
 
-    data <- with_seed_null(params$seed, transform_position(data, trans_x, trans_y))
+    x_aes <- intersect(ggplot_global$x_aes, names(data))
+    y_aes <- intersect(ggplot_global$y_aes, names(data))
+
+    x <- if (length(x_aes) == 0) 0 else data[[x_aes[1]]]
+    y <- if (length(y_aes) == 0) 0 else data[[y_aes[1]]]
+    dummy_data <- data_frame0(x = x, y = y, .size = nrow(data))
+
+    fixed_jitter <- with_seed_null(params$seed, transform_position(dummy_data, trans_x, trans_y))
+    x_jit <- fixed_jitter$x - x
+    y_jit <- fixed_jitter$y - y
+
+    data <- transform_position(data, function(x) x + x_jit, function(x) x + y_jit)
     flip_data(data, params$flipped_aes)
   }
 )

tests/testthat/test-position-jitterdodge.R

@@ -2,3 +2,15 @@ test_that("position_jitterdodge() fails with meaningful error", {
   p <- ggplot(mtcars) + geom_point(aes(disp, mpg), position = 'jitterdodge')
   expect_snapshot_error(ggplot_build(p))
 })
+
+test_that("position_jitterdodge preserves widths", {
+  ld <- layer_data(
+    ggplot(mtcars, aes(factor(cyl), fill = factor(am))) +
+      geom_bar(position = position_jitterdodge())
+  )
+
+  expect_equal(
+    as.numeric(ld$xmax - ld$xmin),
+    rep(0.45, nrow(ld))
+  )
+})