GH-14981: [R] Forward compatibility with dplyr::join_by()

r/R/dplyr-join.R

@@ -136,6 +136,17 @@ handle_join_by <- function(by, x, y) {
   if (is.null(by)) {
     return(set_names(intersect(names(x), names(y))))
   }
+  if (inherits(by, "dplyr_join_by")) {
+    if (!all(by$condition == "==" & by$filter == "none")) {
+      abort(
+        paste0(
+          "Inequality conditions and helper functions ",
+          "are not supported in `join_by()` expressions."
+        )
+      )
+    }
+    by <- set_names(by$y, by$x)
+  }
   stopifnot(is.character(by))
   if (is.null(names(by))) {
     by <- set_names(by)

r/tests/testthat/test-dplyr-join.R

@@ -67,6 +67,39 @@ test_that("left_join `by` args", {
   )
 })
 
+test_that("left_join with join_by", {
+  # only run this test in newer versions of dplyr that include `join_by()`
+  skip_if_not(packageVersion("dplyr") >= "1.0.99.9000")
+
+  compare_dplyr_binding(
+    .input %>%
+      left_join(to_join, join_by(some_grouping)) %>%
+      collect(),
+    left
+  )
+  compare_dplyr_binding(
+    .input %>%
+      left_join(
+        to_join %>%
+          rename(the_grouping = some_grouping),
+          join_by(some_grouping == the_grouping)
+      ) %>%
+      collect(),
+    left
+  )
+
+  compare_dplyr_binding(
+    .input %>%
+      rename(the_grouping = some_grouping) %>%
+      left_join(
+        to_join,
+        join_by(the_grouping == some_grouping)
+      ) %>%
+      collect(),
+    left
+  )
+})
+
 test_that("join two tables", {
   expect_identical(
     arrow_table(left) %>%
@@ -136,6 +169,23 @@ test_that("Error handling", {
   )
 })
 
+test_that("Error handling for unsupported expressions in join_by", {
+  # only run this test in newer versions of dplyr that include `join_by()`
+  skip_if_not(packageVersion("dplyr") >= "1.0.99.9000")
+
+  expect_error(
+    arrow_table(left) %>%
+      left_join(to_join, join_by(some_grouping >= some_grouping)),
+    "not supported"
+  )
+
+  expect_error(
+    arrow_table(left) %>%
+      left_join(to_join, join_by(closest(some_grouping >= some_grouping))),
+    "not supported"
+  )
+})
+
 # TODO: test duplicate col names
 # TODO: casting: int and float columns?