[GitHub] [arrow] jorisvandenbossche commented on a diff in pull request #13281: ARROW-16685: Preserve order of columns in joins

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

jorisvandenbossche commented on code in PR #13281:
URL: https://github.com/apache/arrow/pull/13281#discussion_r886845637


##########
python/pyarrow/_exec_plan.pyx:
##########
@@ -259,13 +259,19 @@ def _perform_join(join_type, left_operand not None, left_keys,
         left_columns = []
     elif join_type == "inner":
         c_join_type = CJoinType_INNER
-        right_columns = set(right_columns) - set(right_keys)
+        right_columns = [
+            col for col in right_columns if col not in set(right_keys)

Review Comment:
   Not that it matters much because it are small numbers anyway, but I was wondering about it: given that `right_keys` is typically a short list, converting it to a set only introduces more overhead.
   
   ```
   In [16]: right_columns = ["a", "b", "c", "d", "e", "f"]
   
   In [17]: right_keys = ["b", "c"]
   
   In [18]: [col for col in right_columns if col not in set(right_keys)]
   Out[18]: ['a', 'd', 'e', 'f']
   
   In [19]: %timeit [col for col in right_columns if col not in set(right_keys)]
   691 ns ± 3.92 ns per loop (mean ± std. dev. of 7 runs, 1,000,000 loops each)
   
   In [20]: %timeit [col for col in right_columns if col not in right_keys]
   353 ns ± 19.1 ns per loop (mean ± std. dev. of 7 runs, 1,000,000 loops each)
   ```



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