positions populate defaults

Author: teunbrand

R/layer.R

@@ -58,8 +58,8 @@
 #'   `NA`, the default, includes if any aesthetics are mapped.
 #'   `FALSE` never includes, and `TRUE` always includes.
 #'   It can also be a named logical vector to finely select the aesthetics to
-#'   display. To include legend keys for all levels, even 
-#'   when no data exists, use `TRUE`.  If `NA`, all levels are shown in legend, 
+#'   display. To include legend keys for all levels, even
+#'   when no data exists, use `TRUE`.  If `NA`, all levels are shown in legend,
 #'   but unobserved levels are omitted.
 #' @param inherit.aes If `FALSE`, overrides the default aesthetics,
 #'   rather than combining with them. This is most useful for helper functions
@@ -437,6 +437,7 @@ Layer <- ggproto("Layer", NULL,
   compute_position = function(self, data, layout) {
     if (empty(data)) return(data_frame0())
 
+    data <- self$position$use_defaults(data, self$aes_params)
     params <- self$position$setup_params(data)
     data <- self$position$setup_data(data, params)
 

R/position-.R

@@ -76,6 +76,28 @@ Position <- ggproto("Position",
       required_aes <- unlist(strsplit(self$required_aes, "|", fixed = TRUE))
     }
     c(union(required_aes, names(self$default_aes)))
+  },
+
+  use_defaults = function(self, data, params = list()) {
+
+    aes <- self$aesthetics()
+    defaults <- self$default_aes
+
+    params <- params[intersect(names(params), aes)]
+    params <- params[setdiff(names(params), names(data))]
+    defaults <- defaults[setdiff(names(defaults), c(names(params), names(data)))]
+
+    if ((length(params) + length(defaults)) < 1) {
+      return(data)
+    }
+
+    new <- compact(lapply(defaults, eval_tidy, data = data))
+    new[names(params)] <- params
+    check_aesthetics(new, nrow(data))
+
+    data[names(new)] <- new
+    data
+
   }
 )