Identity scale doesn't need to train.

Fixes #402

Author: hadley

R/scale-identity.r

@@ -35,8 +35,7 @@ scale_fill_identity <- function(..., guide = "none") {
 #' @rdname scale_identity
 #' @export
 scale_shape_identity <- function(..., guide = "none") {
-  identity_scale(discrete_scale("shape", "identity", identity_pal(), ..., guide = guide))
-    
+  identity_scale(continuous_scale("shape", "identity", identity_pal(), ...,  guide = guide))
 }
 
 #' @rdname scale_identity
@@ -57,7 +56,6 @@ scale_alpha_identity <- function(..., guide = "none") {
 #' @export
 scale_size_identity <- function(..., guide = "none") {
   identity_scale(continuous_scale("size", "identity", identity_pal(), ..., guide = guide))
-    
 }
 
 identity_scale <- function(x) {
@@ -72,5 +70,9 @@ scale_map.identity <- function(scale, x) {
     x
   }
 }
+#' @S3method scale_train identity
+scale_train.identity <- function(scale, x) {
+  # do nothing
+}
 
 icon.identity <- function() textGrob("f(x) = x", gp=gpar(cex=1.2))