From 3b42b984c6265f1ec96f8c684cb31aa1d5a27440 Mon Sep 17 00:00:00 2001
From: Teun van den Brand <tahvdbrand@gmail.com>
Date: Wed, 11 Sep 2024 20:14:45 +0200
Subject: [PATCH] add `key_none()`

---
 NAMESPACE           |  1 +
 R/aaa.R             |  3 +++
 R/key-.R            | 13 +++++++++++++
 man/key_standard.Rd |  7 +++++++
 4 files changed, 24 insertions(+)

diff --git a/NAMESPACE b/NAMESPACE
index 7e9015c..4b41335 100644
--- a/NAMESPACE
+++ b/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)
diff --git a/R/aaa.R b/R/aaa.R
index 565041e..91eb459 100644
--- a/R/aaa.R
+++ b/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")
diff --git a/R/key-.R b/R/key-.R
index 7e1f187..f278377 100644
--- a/R/key-.R
+++ b/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()) {
diff --git a/man/key_standard.Rd b/man/key_standard.Rd
index 83ade01..d78aa16 100644
--- a/man/key_standard.Rd
+++ b/man/key_standard.Rd
@@ -7,6 +7,7 @@
 \alias{key_map}
 \alias{key_minor}
 \alias{key_log}
+\alias{key_none}
 \title{Standard keys}
 \usage{
 key_auto(...)
@@ -30,6 +31,8 @@ key_log(
   labeller = NULL,
   ...
 )
+
+key_none()
 }
 \arguments{
 \item{...}{\code{\link[rlang:topic-data-mask]{<data-masking>}} A set of mappings
@@ -91,6 +94,7 @@ key from major breaks in a scale.
 break positions for minor tick marks.
 \item \code{key_log()} is a function factory whose functions place ticks at intervals
 in log10 space.
+\item \code{key_none()} makes an empty key with no entries.
 }
 }
 \examples{
@@ -113,6 +117,9 @@ key_manual(
 
 # Values from a `<data.frame>`
 key_map(ToothGrowth, aesthetic = unique(supp))
+
+# Empty key
+key_none()
 }
 \seealso{
 Other keys: