Add geom_step(orientation) argument (#5937)

* add `orientiation` to `geom_step()`

* add news bullet

* document

Author: teunbrand

NEWS.md

@@ -1,5 +1,6 @@
 # ggplot2 (development version)
 
+* `geom_step()` now supports the `orientation` argument (@teunbrand, #5936).
 * `position_dodge()` and `position_jitterdodge()` now have a `reverse` argument 
   (@teunbrand, #3610)
 * `coord_radial(r.axis.inside)` can now take a numeric value to control 

R/geom-path.R

@@ -305,7 +305,8 @@ GeomLine <- ggproto("GeomLine", GeomPath,
 #' @rdname geom_path
 geom_step <- function(mapping = NULL, data = NULL, stat = "identity",
                       position = "identity", direction = "hv",
-                      na.rm = FALSE, show.legend = NA, inherit.aes = TRUE, ...) {
+                      na.rm = FALSE, orientation = NA, show.legend = NA,
+                      inherit.aes = TRUE, ...) {
   layer(
     data = data,
     mapping = mapping,
@@ -316,6 +317,7 @@ geom_step <- function(mapping = NULL, data = NULL, stat = "identity",
     inherit.aes = inherit.aes,
     params = list2(
       direction = direction,
+      orientation = orientation,
       na.rm = na.rm,
       ...
     )
@@ -328,11 +330,21 @@ geom_step <- function(mapping = NULL, data = NULL, stat = "identity",
 #' @export
 #' @include geom-path.R
 GeomStep <- ggproto("GeomStep", GeomPath,
+  setup_params = function(data, params) {
+    params$flipped_aes <- has_flipped_aes(data, params, ambiguous = TRUE)
+    params
+  },
+  extra_params = c("na.rm", "orientation"),
   draw_panel = function(data, panel_params, coord,
                         lineend = "butt", linejoin = "round", linemitre = 10,
                         arrow = NULL, arrow.fill = NULL,
-                        direction = "hv") {
+                        direction = "hv", flipped_aes = FALSE) {
+    data <- flip_data(data, flipped_aes)
+    if (isTRUE(flipped_aes)) {
+      direction <- switch(direction, hv = "vh", vh = "hv", direction)
+    }
     data <- dapply(data, "group", stairstep, direction = direction)
+    data <- flip_data(data, flipped_aes)
     GeomPath$draw_panel(
       data, panel_params, coord,
       lineend = lineend, linejoin = linejoin, linemitre = linemitre,