From 69e74305386094cb1fc0b10495d18492cec5b012 Mon Sep 17 00:00:00 2001
From: Andrei <92amartins@gmail.com>
Date: Fri, 22 Sep 2023 11:20:51 -0300
Subject: [PATCH] Improve labeller() behavior for lookup tables (#5432)

---
 NEWS.md                         |  3 +++
 R/labeller.R                    |  6 +++++-
 tests/testthat/test-labellers.R | 12 ++++++++++++
 3 files changed, 20 insertions(+), 1 deletion(-)

diff --git a/NEWS.md b/NEWS.md
index 65572857c7..1d95e88137 100644
--- a/NEWS.md
+++ b/NEWS.md
@@ -1,5 +1,8 @@
 # ggplot2 (development version)
 
+* `labeller()` now handles unspecified entries from lookup tables
+  (@92amartins, #4599).
+
 * `fortify.default()` now accepts a data-frame-like object granted the object
   exhibits healthy `dim()`, `colnames()`, and `as.data.frame()` behaviors
   (@hpages, #5390).
diff --git a/R/labeller.R b/R/labeller.R
index c367a2aa11..8d2a3884be 100644
--- a/R/labeller.R
+++ b/R/labeller.R
@@ -450,7 +450,11 @@ labeller <- function(..., .rows = NULL, .cols = NULL,
       # Apply named labeller one by one
       out <- lapply(names(labels), function(label) {
         if (label %in% names(labellers)) {
-          labellers[[label]](labels[label])[[1]]
+          # Yield custom labels with any NA replaced with original
+          lbls <- labellers[[label]](labels[label])[[1]]
+          ind <- which(is.na(lbls))
+          lbls[ind] <- .default(labels[label])[[1]][ind]
+          lbls
         } else {
           .default(labels[label])[[1]]
         }
diff --git a/tests/testthat/test-labellers.R b/tests/testthat/test-labellers.R
index 0e352e3b26..460349e960 100644
--- a/tests/testthat/test-labellers.R
+++ b/tests/testthat/test-labellers.R
@@ -20,3 +20,15 @@ test_that("labeller function catches overlap in names", {
     )
   expect_snapshot_error(ggplotGrob(p))
 })
+
+test_that("labeller handles badly specified labels from lookup tables", {
+  df <- data_frame0(am = c(0, 1))
+  labs <- labeller(am = c("0" = "Automatic", "11" = "Manual"))
+  expect_equal(labs(df), list(am = c("Automatic", "1")))
+})
+
+test_that("labeller allows cherry-pick some labels", {
+  df <- data_frame0(am = c(0, 1))
+  labs <- labeller(am = c("0" = "Automatic"))
+  expect_equal(labs(df), list(am = c("Automatic", "1")))
+})