Facets drop 'ordered' class (#5704)

* facets always use unordered factors

* add news bullet

Author: teunbrand

NEWS.md

@@ -1,6 +1,8 @@
 
 # ggplot2 (development version)
 
+* When facets coerce the faceting variables to factors, the 'ordered' class
+  is dropped (@teunbrand, #5666).
 * `update_geom_defaults()` and `update_stat_defaults()` have a reset mechanism
   when using `new = NULL` and invisible return the previous defaults (#4993).
 * `coord_map()` and `coord_polar()` throw informative warnings when used

R/facet-grid-.R

@@ -325,9 +325,9 @@ FacetGrid <- ggproto("FacetGrid", Facet,
       # Special case of no faceting
       data$PANEL <- NO_PANEL
     } else {
-      facet_vals[] <- lapply(facet_vals[], as.factor)
+      facet_vals[] <- lapply(facet_vals[], as_unordered_factor)
       facet_vals[] <- lapply(facet_vals[], addNA, ifany = TRUE)
-      layout[] <- lapply(layout[], as.factor)
+      layout[] <- lapply(layout[], as_unordered_factor)
 
       keys <- join_keys(facet_vals, layout, by = vars)
 

R/facet-wrap.R

@@ -228,8 +228,8 @@ FacetWrap <- ggproto("FacetWrap", Facet,
     }
 
     facet_vals <- eval_facets(vars, data, params$.possible_columns)
-    facet_vals[] <- lapply(facet_vals[], as.factor)
-    layout[] <- lapply(layout[], as.factor)
+    facet_vals[] <- lapply(facet_vals[], as_unordered_factor)
+    layout[] <- lapply(layout[], as_unordered_factor)
 
     missing_facets <- setdiff(names(vars), names(facet_vals))
     if (length(missing_facets) > 0) {

R/utilities.R

@@ -811,3 +811,9 @@ deprecate_warn0 <- function(..., user_env = NULL) {
   user_env <- user_env %||% getOption("ggplot2_plot_env") %||% caller_env(2)
   lifecycle::deprecate_warn(..., user_env = user_env)
 }
+
+as_unordered_factor <- function(x) {
+  x <- as.factor(x)
+  class(x) <- setdiff(class(x), "ordered")
+  x
+}