Add ggplot_add.by method (#3425)

Fixes #2734

Author: Maschette

NAMESPACE

@@ -49,6 +49,7 @@ S3method(ggplot_add,Coord)
 S3method(ggplot_add,Facet)
 S3method(ggplot_add,Layer)
 S3method(ggplot_add,Scale)
+S3method(ggplot_add,by)
 S3method(ggplot_add,data.frame)
 S3method(ggplot_add,default)
 S3method(ggplot_add,guides)

NEWS.md

@@ -1,5 +1,7 @@
 # ggplot2 (development version)
 
+* Added function `ggplot_add.by()` for lists created with `by()` (#2734, @Maschette)
+
 * `ggdep()` was deprecated (@perezp44, #3382).
 
 * Added weight aesthetic option to `stat_density()` and made scaling of 

R/plot-construction.r

@@ -151,6 +151,11 @@ ggplot_add.list <- function(object, plot, object_name) {
   }
   plot
 }
+#' @export
+ggplot_add.by <- function(object, plot, object_name) {
+  ggplot_add.list(object, plot, object_name)
+}
+
 #' @export
 ggplot_add.Layer <- function(object, plot, object_name) {
   plot$layers <- append(plot$layers, object)