Add marginal dist. to PPD plots

NEWS.md

@@ -1,5 +1,6 @@
 # bayesplot (development version)
 
+* New `show_marginal` argument to `ppd_*()` functions to show the PPD - the marginal predictive distribution by @mattansb (#425)
 * Documentation added for all exported `*_data()` functions (#209)
 * Improved documentation for `binwidth`, `bins`, and `breaks` arguments to clarify they are passed to `ggplot2::geom_area()` and `ggdist::stat_dots()` in addition to `ggplot2::geom_histogram()`
 * Improved documentation for `freq` argument to clarify it applies to frequency polygons in addition to histograms

R/helpers-gg.R

@@ -125,22 +125,26 @@ scale_fill_ppc <-
 
 scale_color_ppd <-
   function(name = NULL,
-           values = get_color("mh"),
-           labels = ypred_label(),
+           values = NULL,
+           labels = NULL,
            ...) {
-    scale_color_ppc(name = name,
-                    values = values,
-                    labels = labels,
-                    ...)
+    scale_color_ppc(
+      name = name,
+      values = values %||% setNames(get_color(c("dh", "mh")), nm = c("PPD", "ypred")),
+      labels = labels %||% ypred_label(),
+      ...
+    )
   }
 
 scale_fill_ppd <-
   function(name = NULL,
-           values = get_color("m"),
-           labels = ypred_label(),
+           values = NULL,
+           labels = NULL,
            ...) {
-    scale_fill_ppc(name = name,
-                   values = values,
-                   labels = labels,
-                   ...)
+    scale_fill_ppc(
+      name = name,
+      values = values %||% setNames(get_color(c("d", "m")), nm = c("PPD", "ypred")),
+      labels = labels %||% ypred_label(),
+      ...
+    )
   }

R/helpers-ppc.R

@@ -594,4 +594,9 @@ u_scale <- function(x) {
 create_rep_ids <- function(ids) paste('italic(y)[rep] (', ids, ")")
 y_label <- function() expression(italic(y))
 yrep_label <- function() expression(italic(y)[rep])
-ypred_label <- function() expression(italic(y)[pred])
+ypred_label <- function() {
+  c(
+    PPD = "PPD",
+    ypred = expression(italic(y)[pred])
+  )
+}