Add default to stat_summary.

Fixes #1386

Author: hadley

NEWS.md

@@ -38,7 +38,8 @@
 
 * New `stat_summary_bin()` works like `stat_summary()` but on binned data. 
   It's a generalisation of `stat_bin()` that can compute any aggregate,
-  not just counts (#1274).
+  not just counts (#1274). Both default to `mean_se()` if no aggregation
+  functions are supplied (#1386).
 
 * Layers are now much stricter about their arguments - you will get an error
   if you've supplied an argument that isn't an aesthetic or a parameter.

R/stat-summary-bin.R

@@ -59,7 +59,7 @@ make_summary_fun <- function(fun.data, fun.y, fun.ymax, fun.ymin, fun.args) {
     function(df) {
       do.call(fun.data, c(list(quote(df$y)), fun.args))
     }
-  } else {
+  } else if (!is.null(fun.y) || !is.null(fun.ymax) || !is.null(fun.ymin)) {
     # Three functions that take vectors as inputs
 
     call_f <- function(fun, x) {
@@ -74,5 +74,10 @@ make_summary_fun <- function(fun.data, fun.y, fun.ymax, fun.ymin, fun.args) {
         ymax = call_f(fun.ymax, df$y)
       )
     }
+  } else {
+    message("No summary function supplied, defaulting to `mean_se()")
+    function(df) {
+      mean_se(df$y)
+    }
   }
 }

R/stat-summary.r

@@ -31,6 +31,9 @@
 #' number, but is somewhat less flexible. If your summary function computes
 #' multiple values at once (e.g. ymin and ymax), use \code{fun.data}.
 #'
+#' If no aggregation functions are suppled, will default to
+#' \code{\link{mean_se}}.
+#'
 #' @param fun.data A function that is given the complete data and should
 #'   return a data frame with variables \code{ymin}, \code{y}, and \code{ymax}.
 #' @param fun.ymin,fun.y,fun.ymax Alternatively, supply three individual