Adressing Hadley Wickham's suggestions to #927

NEWS

@@ -1,6 +1,10 @@
 ggplot2 0.9.3.1.99
 ----------------------------------------------------------------
 
+* `geom_boxplot` gain new `varwidth` argument for controlling whether or not 
+  the width of boxplots should be proportional to the size of the groups 
+  (@tsieger, #927).
+
 * Allow specifying only one of the limits in a scale and use the automatic
   calculation of the other limit by passing NA to to the limit function,
   `xlim()` or `ylim()` (@jimhester, #557).

R/geom-boxplot.r

@@ -35,7 +35,7 @@
 #' @param varwidth if \code{FALSE} (default) make a standard box plot. If
 #'    \code{TRUE}, boxes are drawn with widths proportional to the
 #'    square-roots of the number of observations in the groups (possibly
-#'    weighted).
+#'    weighted, using the \code{weight} aesthetic).
 #' @export
 #'
 #' @references McGill, R., Tukey, J. W. and Larsen, W. A. (1978) Variations of
@@ -126,23 +126,20 @@ GeomBoxplot <- proto(Geom, {
       df$ymax_final <- pmax(out_max, df$ymax)
     }
 
-    # if varwidth not requested or not available, don't use it
-    if(is.null(params) || is.null(params$varwidth) || !params$varwidth || is.null(df$relvarwidth)) {
-        if (is.null(df$relvarwidth)) {
-          transform(df,
-            xmin = x - width / 2, xmax = x + width / 2, width = NULL
-          )
-        } else {
-          transform(df,
-            xmin = x - width / 2, xmax = x + width / 2, width = NULL, relvarwidth = NULL
-          )
-        }
+    # if `varwidth` not requested or not available, don't use it
+    if (is.null(params) || is.null(params$varwidth) || !params$varwidth || is.null(df$relvarwidth)) {
+      df$xmin <- df$x - df$width / 2
+      df$xmax <- df$x + df$width / 2
     } else {
-      transform(df,
-        xmin = x - relvarwidth * width / 2, xmax = x + relvarwidth * width / 2, width = NULL, relvarwidth = NULL
-      )
+      # make `relvarwidth` relative to the size of the largest group
+      df$relvarwidth <- df$relvarwidth / max(df$relvarwidth)
+      df$xmin <- df$x - df$relvarwidth * df$width / 2
+      df$xmax <- df$x + df$relvarwidth * df$width / 2
     }
+    df$width <- NULL
+    if (!is.null(df$relvarwidth)) df$relvarwidth <- NULL
 
+    df
   }
 
   draw <- function(., data, ..., fatten = 2, outlier.colour = NULL, outlier.shape = NULL, outlier.size = 2,

man/geom_boxplot.Rd

@@ -27,7 +27,8 @@ geom_boxplot(mapping = NULL, data = NULL, stat = "boxplot",
   \item{varwidth}{if \code{FALSE} (default) make a standard
   box plot. If \code{TRUE}, boxes are drawn with widths
   proportional to the square-roots of the number of
-  observations in the groups (possibly weighted).}
+  observations in the groups (possibly weighted, using the
+  \code{weight} aesthetic).}
 
   \item{mapping}{The aesthetic mapping, usually constructed
   with \code{\link{aes}} or \code{\link{aes_string}}. Only