don't use xy.coords because it does not retain class

Author: Lindsay Carr

R/set_args.R

@@ -15,8 +15,11 @@ set_args <- function(fun.name, ..., custom.config = FALSE, package='graphics'){
   user_args <- function_args(name=fun.name, package=package, ...)
 
   if(fun.name %in% c('points', 'lines')){
-    xy_args <- xy.coords(x = user_args[['x']], y = user_args[['y']])
-    user_args <- append_replace(user_args, xy_args)
+    if(!is.null(user_args[['x']]) & is.null(user_args[['y']])){
+      xy_args <- list(x = seq_along(user_args[['x']]),
+                      y = user_args[['x']])
+      user_args <- append_replace(user_args, xy_args)
+    }
   }
 
   indicesToAdd <- !(names(config_args) %in% names(user_args))