[GitHub] [arrow] nealrichardson commented on a diff in pull request #13621: ARROW-17085: [R] group_vars() should not return NULL

[GitBox <gi...@apache.org>]

nealrichardson commented on code in PR #13621:
URL: https://github.com/apache/arrow/pull/13621#discussion_r922162323


##########
r/tests/testthat/test-metadata.R:
##########
@@ -383,6 +383,7 @@ test_that("grouped_df metadata is recorded (efficiently)", {
   grouped_tab <- Table$create(grouped)
   expect_r6_class(grouped_tab, "Table")
   expect_equal(grouped_tab$r_metadata$attributes$.group_vars, "a")
+  expect_equal(grouped_tab$metadata$r$attributes$.group_vars, "a")

Review Comment:
   L385 and L386 are the same thing, we don't need both tests (pick one, either is fine)



##########
r/R/dplyr-group-by.R:
##########
@@ -58,13 +58,13 @@ group_by.arrow_dplyr_query <- function(.data,
 group_by.Dataset <- group_by.ArrowTabular <- group_by.RecordBatchReader <- group_by.arrow_dplyr_query
 
 groups.arrow_dplyr_query <- function(x) syms(dplyr::group_vars(x))
-groups.Dataset <- groups.ArrowTabular <- groups.RecordBatchReader <- function(x) NULL
+groups.Dataset <- groups.ArrowTabular <- groups.RecordBatchReader <- function(x) syms(dplyr::group_vars(x))

Review Comment:
   We know they're empty so we can simplify this
   
   ```suggestion
   groups.Dataset <- groups.ArrowTabular <- groups.RecordBatchReader <- function(x) list()
   ```
   
   The result is the same:
   
   ```
   > identical(rlang::syms(character(0)), list())
   [1] TRUE
   ```



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