add seed argument to position_jitterdodge (#2445)

NEWS.md

@@ -195,8 +195,9 @@ up correct aspect ratio, and draws a graticule.
   default), or ensure that the width of a `single` element is preserved
   (what many people want) (#1935).
 
-* `position_jitter()` gains a `seed` argument that allows specifying a random 
-  seed for reproducible jittering (#1996, @krlmlr).
+* `position_jitter()` and `position_jitterdodge()` gain a `seed` argument that
+  allows specifying a random seed for reproducible jittering (@krlmlr, #1996
+  and @slowkow, #2445).
 
 * `stat_density()` has better behaviour if all groups are dropped because they
   are too small (#2282).

R/position-jitterdodge.R

@@ -10,19 +10,24 @@
 #' @param jitter.height degree of jitter in y direction. Defaults to 0.
 #' @param dodge.width the amount to dodge in the x direction. Defaults to 0.75,
 #'   the default `position_dodge()` width.
+#' @inheritParams position_jitter
 #' @export
 #' @examples
 #' dsub <- diamonds[ sample(nrow(diamonds), 1000), ]
 #' ggplot(dsub, aes(x = cut, y = carat, fill = clarity)) +
 #'   geom_boxplot(outlier.size = 0) +
 #'   geom_point(pch = 21, position = position_jitterdodge())
 position_jitterdodge <- function(jitter.width = NULL, jitter.height = 0,
-                                 dodge.width = 0.75) {
+                                 dodge.width = 0.75, seed = NA) {
+  if (!is.null(seed) && is.na(seed)) {
+    seed <- sample.int(.Machine$integer.max, 1L)
+  }
 
   ggproto(NULL, PositionJitterdodge,
     jitter.width = jitter.width,
     jitter.height = jitter.height,
-    dodge.width = dodge.width
+    dodge.width = dodge.width,
+    seed = seed
   )
 }
 
@@ -50,19 +55,18 @@ PositionJitterdodge <- ggproto("PositionJitterdodge", Position,
     list(
       dodge.width = self$dodge.width,
       jitter.height = self$jitter.height,
-      jitter.width = width / (ndodge + 2)
+      jitter.width = width / (ndodge + 2),
+      seed = self$seed
     )
   },
 
-
   compute_panel = function(data, params, scales) {
     data <- collide(data, params$dodge.width, "position_jitterdodge", pos_dodge,
       check.width = FALSE)
 
-    # then jitter
-    transform_position(data,
-      if (params$jitter.width > 0) function(x) jitter(x, amount = params$jitter.width),
-      if (params$jitter.height > 0) function(x) jitter(x, amount = params$jitter.height)
-    )
+    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)
+
+    with_seed_null(params$seed, transform_position(data, trans_x, trans_y))
   }
 )