🦃 Add ggplot2 method for grouped df

*gobble* fixes #2351 *gobble*

NAMESPACE

@@ -37,6 +37,7 @@ S3method(fortify,summary.glht)
 S3method(fortify,tbl)
 S3method(ggplot,data.frame)
 S3method(ggplot,default)
+S3method(ggplot,grouped_df)
 S3method(ggplot_add,"NULL")
 S3method(ggplot_add,Coord)
 S3method(ggplot_add,Facet)

NEWS.md

@@ -242,6 +242,10 @@ up correct aspect ratio, and draws a graticule.
 
 * `fortify()` gains a method for tbls (@karawoo, #2218)
 
+* `ggplot` gains a method for `grouped_df`s that adds a `.group` variable,
+  which computes a unique value for each group, and automatically sets
+  the group aesthetic to use that variable (#2351).
+
 * `ggproto()` produces objects with class `c("ggproto", "gg")`, allowing for
   a more informative error message when adding layers, scales, or other ggproto 
   objects (@jrnold, #2056).

R/plot.r

@@ -106,6 +106,16 @@ ggplot.data.frame <- function(data, mapping = aes(), ...,
   p
 }
 
+#' @export
+ggplot.grouped_df <- function(data, mapping = aes(), ...,
+                               environment = parent.frame()) {
+
+  data$.group <- dplyr::group_indices(data)
+  mapping$group <- mapping$group %||% quote(.group)
+
+  ggplot.data.frame(data, mapping = mapping, ..., environment = environment)
+}
+
 plot_clone <- function(plot) {
   p <- plot
   p$scales <- plot$scales$clone()