From 52b067eb3fc59faf232aea1c52d435b16d145430 Mon Sep 17 00:00:00 2001
From: Nic Crane <thisisnic@gmail.com>
Date: Wed, 4 Jan 2023 19:08:37 +0000
Subject: [PATCH] GH-14907: [R] right_join() function does not produce the
 expected outcome (#15077)

* Closes: #14907

Authored-by: Nic Crane <thisisnic@gmail.com>
Signed-off-by: Will Jones <willjones127@gmail.com>
---
 r/R/dplyr-join.R                   |   9 ++-
 r/tests/testthat/test-dplyr-join.R | 100 ++++++++++++++++++-----------
 2 files changed, 71 insertions(+), 38 deletions(-)

diff --git a/r/R/dplyr-join.R b/r/R/dplyr-join.R
index 5e2b6084b21e0..fad44b5ef2751 100644
--- a/r/R/dplyr-join.R
+++ b/r/R/dplyr-join.R
@@ -35,8 +35,13 @@ do_join <- function(x,
 
   # For outer joins, we need to output the join keys on both sides so we
   # can coalesce them afterwards.
-  left_output <- names(x)
-  right_output <- if (keep || join_type == "FULL_OUTER") {
+  left_output <- if (!keep && join_type == "RIGHT_OUTER") {
+    setdiff(names(x), by)
+  } else {
+    names(x)
+  }
+
+  right_output <- if (keep || join_type %in% c("FULL_OUTER", "RIGHT_OUTER")) {
     names(y)
   } else {
     setdiff(names(y), by)
diff --git a/r/tests/testthat/test-dplyr-join.R b/r/tests/testthat/test-dplyr-join.R
index cae741ae27652..5c6798aeebc18 100644
--- a/r/tests/testthat/test-dplyr-join.R
+++ b/r/tests/testthat/test-dplyr-join.R
@@ -21,8 +21,8 @@ left <- example_data
 left$some_grouping <- rep(c(1, 2), 5)
 
 to_join <- tibble::tibble(
-  some_grouping = c(1, 2),
-  capital_letters = c("A", "B"),
+  some_grouping = c(1, 2, 3),
+  capital_letters = c("A", "B", "C"),
   another_column = TRUE
 )
 
@@ -140,42 +140,64 @@ test_that("Error handling", {
 # TODO: casting: int and float columns?
 
 test_that("right_join", {
-  for (keep in c(TRUE, FALSE)) {
-    compare_dplyr_binding(
-      .input %>%
-        right_join(to_join, by = "some_grouping", keep = !!keep) %>%
-        collect(),
-      left
-    )
-  }
+  compare_dplyr_binding(
+    .input %>%
+      right_join(to_join, by = "some_grouping", keep = TRUE) %>%
+      collect(),
+    left
+  )
+
+  compare_dplyr_binding(
+    .input %>%
+      right_join(to_join, by = "some_grouping", keep = FALSE) %>%
+      collect(),
+    left
+  )
 })
 
 test_that("inner_join", {
-  for (keep in c(TRUE, FALSE)) {
-    compare_dplyr_binding(
-      .input %>%
-        inner_join(to_join, by = "some_grouping", keep = !!keep) %>%
-        collect(),
-      left
-    )
-  }
+  compare_dplyr_binding(
+    .input %>%
+      inner_join(to_join, by = "some_grouping", keep = TRUE) %>%
+      collect(),
+    left
+  )
+
+  compare_dplyr_binding(
+    .input %>%
+      inner_join(to_join, by = "some_grouping", keep = FALSE) %>%
+      collect(),
+    left
+  )
 })
 
 test_that("full_join", {
-  for (keep in c(TRUE, FALSE)) {
-    compare_dplyr_binding(
-      .input %>%
-        full_join(to_join, by = "some_grouping", keep = !!keep) %>%
-        collect(),
-      left
-    )
-  }
+  compare_dplyr_binding(
+    .input %>%
+      full_join(to_join, by = "some_grouping", keep = TRUE) %>%
+      collect(),
+    left
+  )
+
+  compare_dplyr_binding(
+    .input %>%
+      full_join(to_join, by = "some_grouping", keep = FALSE) %>%
+      collect(),
+    left
+  )
 })
 
 test_that("semi_join", {
   compare_dplyr_binding(
     .input %>%
-      semi_join(to_join, by = "some_grouping") %>%
+      semi_join(to_join, by = "some_grouping", keep = TRUE) %>%
+      collect(),
+    left
+  )
+
+  compare_dplyr_binding(
+    .input %>%
+      semi_join(to_join, by = "some_grouping", keep = FALSE) %>%
       collect(),
     left
   )
@@ -358,13 +380,19 @@ test_that("full joins handle keep", {
     z = 6:10
   )
 
-  for (keep in c(TRUE, FALSE)) {
-    compare_dplyr_binding(
-      .input %>%
-        full_join(full_data_df, by = c("y", "x"), keep = !!keep) %>%
-        arrange(index) %>%
-        collect(),
-      small_dataset_df
-    )
-  }
+  compare_dplyr_binding(
+    .input %>%
+      full_join(full_data_df, by = c("y", "x"), keep = TRUE) %>%
+      arrange(index) %>%
+      collect(),
+    small_dataset_df
+  )
+
+  compare_dplyr_binding(
+    .input %>%
+      full_join(full_data_df, by = c("y", "x"), keep = FALSE) %>%
+      arrange(index) %>%
+      collect(),
+    small_dataset_df
+  )
 })