Make layer() accept formula notation for data argument (#3245)

Author: yutannihilation

NAMESPACE

@@ -32,6 +32,7 @@ S3method(fortify,cld)
 S3method(fortify,confint.glht)
 S3method(fortify,data.frame)
 S3method(fortify,default)
+S3method(fortify,formula)
 S3method(fortify,glht)
 S3method(fortify,grouped_df)
 S3method(fortify,lm)

NEWS.md

@@ -138,6 +138,9 @@ core developer team.
   now renamed to always match the ones of `Stat$compute_layer()` and
   `Position$compute_layer()` (@yutannihilation, #3202).
 
+* `geom_*()` and `stat_*()` now accepts purrr-style lambda notation
+  (@yutannihilation, #3138).
+
 # ggplot2 3.1.0
 
 ## Breaking changes

R/fortify.r

@@ -26,6 +26,9 @@ fortify.tbl <- function(model, data, ...) {
 fortify.NULL <- function(model, data, ...) waiver()
 #' @export
 fortify.function <- function(model, data, ...) model
+# accept purrr-style lambda notation
+#' @export
+fortify.formula <- function(model, data, ...) as_function(model)
 #' @export
 fortify.grouped_df <- function(model, data, ...) {
   if (!requireNamespace("dplyr", quietly = TRUE)) {

R/layer.r

@@ -22,7 +22,8 @@
 #'
 #'    A `function` will be called with a single argument,
 #'    the plot data. The return value must be a `data.frame`, and
-#'    will be used as the layer data.
+#'    will be used as the layer data. A `function` can be created
+#'    from a `formula` (e.g. `~ head(.x, 10)`).
 #' @param geom The geometric object to use display the data
 #' @param stat The statistical transformation to use on the data for this
 #'    layer, as a string.