x and y should be optional in aes_string

Author: hadley

R/aes.r

@@ -100,8 +100,8 @@ is_position_aes <- function(vars) {
 #' aes(mpg, wt, col = cyl, fill = NULL)
 #' aes_string("mpg", "wt", col = "cyl", fill = NULL)
 #' aes_q(quote(mpg), quote(wt), col = quote(cyl), fill = NULL)
-aes_string <- function(x, y, ...) {
-  mapping <- list(x = x, y = y, ...)
+aes_string <- function(x = NULL, y = NULL, ...) {
+  mapping <- c(compact(list(x = x, y = y)), list(...))
   mapping[vapply(mapping, is.null, logical(1))] <- "NULL"
 
   parsed <- lapply(mapping, function(x) parse(text = x)[[1]])

man/aes_string.Rd

@@ -4,7 +4,7 @@
 \alias{aes_string}
 \title{Generate aesthetic mappings from a string/quoted objects}
 \usage{
-aes_string(x, y, ...)
+aes_string(x = NULL, y = NULL, ...)
 
 aes_q(x, y, ...)
 }