add key_none()

NAMESPACE

@@ -51,6 +51,7 @@ export(key_log)
 export(key_manual)
 export(key_map)
 export(key_minor)
+export(key_none)
 export(key_range_auto)
 export(key_range_manual)
 export(key_range_map)

R/aaa.R

@@ -25,6 +25,9 @@ standard_extract_key <- function(scale, aesthetic, key, ...) {
   if (is.function(key)) {
     key <- key(scale, aesthetic)
   }
+  if (is_empty(key)) {
+    return(key)
+  }
   if ("aesthetic" %in% names(key)) {
     key$aesthetic <-
       scale_transform(key$aesthetic, scale, map = TRUE, "aesthetic")

R/key-.R

@@ -15,6 +15,7 @@
 #'   break positions for minor tick marks.
 #' * `key_log()` is a function factory whose functions place ticks at intervals
 #'   in log10 space.
+#' * `key_none()` makes an empty key with no entries.
 #'
 #' @param aesthetic,value A vector of values for the guide to represent
 #'   equivalent to the `breaks` argument in scales. The `aesthetic` will be
@@ -75,6 +76,9 @@
 #'
 #' # Values from a `<data.frame>`
 #' key_map(ToothGrowth, aesthetic = unique(supp))
+#'
+#' # Empty key
+#' key_none()
 NULL
 
 #' @rdname key_standard
@@ -171,6 +175,15 @@ key_log <- function(
   }
 }
 
+#' @rdname key_standard
+#' @export
+key_none <- function() {
+  new_data_frame(
+    list(aesthetic = logical(), .value = logical(), .label = character()),
+    n = 0L, class = c("key_standard", "key_guide")
+  )
+}
+
 # Helpers -----------------------------------------------------------------
 
 validate_key_types <- function(key, call = caller_env()) {