Improve stat_ecdf padding.

Fixes #1467

Author: hadley

NEWS.md

@@ -1,5 +1,8 @@
 # ggplot2 2.0.0.9000
 
+* `stat_ecdf()` does a better job of adding padding to -Inf/Inf, and gains
+  an argument `pad` to suppress the padding if not needed (#1467).
+
 * Multipanel empty data is correctly plotted, rather than throwing an unhelpful 
   error (#1445).
 

R/stat-ecdf.r

@@ -5,6 +5,8 @@
 #'    a warning.  If \code{TRUE} silently removes missing values.
 #' @param n if NULL, do not interpolate. If not NULL, this is the number
 #'   of points to interpolate with.
+#' @param pad If \code{TRUE}, pad the ecdf with additional points (-Inf, 0)
+#'   and (Inf, 1)
 #' @section Computed variables:
 #' \describe{
 #'   \item{x}{x in data}
@@ -22,7 +24,8 @@
 #' ggplot(df, aes(x, colour = g)) + stat_ecdf()
 #' }
 stat_ecdf <- function(mapping = NULL, data = NULL, geom = "step",
-                      position = "identity", n = NULL, na.rm = FALSE,
+                      position = "identity", n = NULL,
+                      pad = TRUE, na.rm = FALSE,
                       show.legend = NA, inherit.aes = TRUE, ...) {
   layer(
     data = data,
@@ -46,31 +49,20 @@ stat_ecdf <- function(mapping = NULL, data = NULL, geom = "step",
 #' @usage NULL
 #' @export
 StatEcdf <- ggproto("StatEcdf", Stat,
-  compute_group = function(data, scales, n = NULL) {
-
+  compute_group = function(data, scales, n = NULL, pad = TRUE) {
     # If n is NULL, use raw values; otherwise interpolate
     if (is.null(n)) {
-      xvals <- unique(data$x)
+      x <- unique(data$x)
     } else {
-      xvals <- seq(min(data$x), max(data$x), length.out = n)
+      x <- seq(min(data$x), max(data$x), length.out = n)
     }
 
-    y <- ecdf(data$x)(xvals)
-
-    # make point with y = 0, from plot.stepfun
-    rx <- range(xvals)
-    if (length(xvals) > 1L) {
-      dr <- max(0.08 * diff(rx), median(diff(xvals)))
-    } else {
-      dr <- abs(xvals)/16
+    if (pad) {
+      x <- c(-Inf, x, Inf)
     }
+    y <- ecdf(data$x)(x)
 
-    x0 <- rx[1] - dr
-    x1 <- rx[2] + dr
-    y0 <- 0
-    y1 <- 1
-
-    data.frame(x = c(x0, xvals, x1), y = c(y0, y, y1))
+    data.frame(x = x, y = y)
   },
 
   default_aes = aes(y = ..y..),