Manual stat (#6103)

* write `stat_manual()`

* document

* add test

* add news bullet

* fix examples with double point layers

* add to pkgdown index

* document `geom` slot

Author: teunbrand

DESCRIPTION

@@ -254,6 +254,7 @@ Collate:
     'stat-ellipse.R'
     'stat-function.R'
     'stat-identity.R'
+    'stat-manual.R'
     'stat-qq-line.R'
     'stat-qq.R'
     'stat-quantilemethods.R'

NAMESPACE

@@ -265,6 +265,7 @@ export(StatEcdf)
 export(StatEllipse)
 export(StatFunction)
 export(StatIdentity)
+export(StatManual)
 export(StatQq)
 export(StatQqLine)
 export(StatQuantile)
@@ -691,6 +692,7 @@ export(stat_ecdf)
 export(stat_ellipse)
 export(stat_function)
 export(stat_identity)
+export(stat_manual)
 export(stat_qq)
 export(stat_qq_line)
 export(stat_quantile)

NEWS.md

@@ -1,5 +1,6 @@
 # ggplot2 (development version)
 
+* New stat: `stat_manual()` for arbitrary computations (@teunbrand, #3501)
 * Reversal of a dimension, typically 'x' or 'y', is now controlled by the 
   `reverse` argument in `coord_cartesian()`, `coord_fixed()`, `coord_radial()`
   and `coord_sf()`. In `coord_radial()`, this replaces the older `direction` 

R/stat-manual.R

@@ -0,0 +1,131 @@
+
+#' Manually compute transformations
+#'
+#' `stat_manual()` takes a function that computes a data transformation for
+#' every group.
+#'
+#' @inheritParams layer
+#' @inheritParams geom_point
+#' @param fun Function that takes a data frame as input and returns a data
+#'   frame or data frame-like list as output. The default (`identity()`) returns
+#'   the data unchanged.
+#' @param args A list of arguments to pass to the function given in `fun`.
+#'
+#' @eval rd_aesthetics("stat", "manual")
+#' @section Aesthetics:
+#' Input aesthetics are determined by the `fun` argument. Output aesthetics must
+#' include those required by `geom`. Any aesthetic that is constant within a
+#' group will be preserved even if dropped by `fun`.
+#'
+#' @export
+#'
+#' @examples
+#' # A standard scatterplot
+#' p <- ggplot(mtcars, aes(disp, mpg, colour = factor(cyl))) +
+#'   geom_point()
+#'
+#' # The default just displays points as-is
+#' p + stat_manual()
+#'
+#' # Using a custom function
+#' make_hull <- function(data) {
+#'   hull <- chull(x = data$x, y = data$y)
+#'   data.frame(x = data$x[hull], y = data$y[hull])
+#' }
+#'
+#' p + stat_manual(
+#'   geom = "polygon",
+#'   fun  = make_hull,
+#'   fill = NA
+#' )
+#'
+#' # Using the `with` function with quoting
+#' p + stat_manual(
+#'   fun  = with,
+#'   args = list(expr = quote({
+#'     hull <- chull(x, y)
+#'     list(x = x[hull], y = y[hull])
+#'   })),
+#'   geom = "polygon", fill = NA
+#' )
+#'
+#' # Using the `transform` function with quoting
+#' p + stat_manual(
+#'   geom = "segment",
+#'   fun  = transform,
+#'   args = list(
+#'     xend = quote(mean(x)),
+#'     yend = quote(mean(y))
+#'   )
+#' )
+#'
+#' # Using dplyr verbs with `vars()`
+#' if (requireNamespace("dplyr", quietly = TRUE)) {
+#'
+#'   # Get centroids with `summarise()`
+#'   p + stat_manual(
+#'     size = 10, shape = 21,
+#'     fun  = dplyr::summarise,
+#'     args = vars(x = mean(x), y = mean(y))
+#'   )
+#'
+#'   # Connect to centroid with `mutate`
+#'   p + stat_manual(
+#'     geom = "segment",
+#'     fun  = dplyr::mutate,
+#'     args = vars(xend = mean(x), yend = mean(y))
+#'   )
+#'
+#'   # Computing hull with `reframe()`
+#'   p + stat_manual(
+#'     geom = "polygon", fill = NA,
+#'     fun  = dplyr::reframe,
+#'     args = vars(hull = chull(x, y), x = x[hull], y = y[hull])
+#'   )
+#' }
+stat_manual <- function(
+    mapping = NULL,
+    data = NULL,
+    geom = "point",
+    position = "identity",
+    ...,
+    fun = identity,
+    args = list(),
+    na.rm = FALSE,
+    show.legend = NA,
+    inherit.aes = TRUE) {
+
+  layer(
+    data = data,
+    mapping = mapping,
+    stat = StatManual,
+    geom = geom,
+    position = position,
+    show.legend = show.legend,
+    inherit.aes = inherit.aes,
+    params = list2(
+      na.rm = na.rm,
+      fun = fun,
+      args = args,
+      ...
+    )
+  )
+}
+
+#' @rdname ggplot2-ggproto
+#' @format NULL
+#' @usage NULL
+#' @export
+StatManual <- ggproto(
+  "StatManual", Stat,
+
+  setup_params = function(data, params) {
+    params$fun <- allow_lambda(params$fun)
+    check_function(params$fun, arg = "fun")
+    params
+  },
+
+  compute_group = function(data, scales, fun = identity, args = list()) {
+    as_gg_data_frame(inject(fun(data, !!!args)))
+  }
+)

_pkgdown.yml

@@ -68,6 +68,7 @@ reference:
   - stat_summary_bin
   - stat_unique
   - stat_sf_coordinates
+  - stat_manual
   - after_stat
 
 - subtitle: Position adjustment