[GitHub] [arrow] wesm commented on a diff in pull request #13583: ARROW-16807: [C++][R] count distinct incorrectly merges state

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

wesm commented on code in PR #13583:
URL: https://github.com/apache/arrow/pull/13583#discussion_r920552152


##########
r/tests/testthat/test-dplyr-summarize.R:
##########
@@ -218,6 +218,15 @@ test_that("Group by any/all", {
   )
 })
 
+test_that("n_distinct() with many batches", {
+	tf <- tempfile()

Review Comment:
   Use spaces instead of tabs



##########
cpp/src/arrow/util/hashing.h:
##########
@@ -428,6 +428,22 @@ class ScalarMemoTable : public MemoTable {
         value, [](int32_t i) {}, [](int32_t i) {}, out_memo_index);
   }
 
+  Status MaybeInsert(const Scalar& value) {

Review Comment:
   Or at least implement this new API with `GetOrInsert` — the `Status GetOrInsert(const Scalar& value, int32_t* out_memo_index)` version should generate the same code more or less as this (with the exception of the unused index)



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