[GitHub] [arrow] bkietz commented on a diff in pull request #37174: GH-37173: [C++][Format] C-export/import Run-End Encoded Arrays

["bkietz (via GitHub)" <gi...@apache.org>]

bkietz commented on code in PR #37174:
URL: https://github.com/apache/arrow/pull/37174#discussion_r1295916233


##########
docs/source/format/CDataInterface.rst:
##########
@@ -217,6 +217,8 @@ names and types of child fields are read from the child arrays.
 +------------------------+---------------------------------------------------+------------+
 | ``+us:I,J,...``        | sparse union with type ids I,J...                 |            |
 +------------------------+---------------------------------------------------+------------+
+| ``+r``                 | run-end encoded                                   |            |

Review Comment:
   I think reiteration is warranted in this case, something like:
   ```suggestion
   | ``+r``                 | run-end encoded                                   | \(3)       |
   ```
   ```rst
   (3)
      As specified in the Arrow columnar format, the run end encoded type two children where the first is the (integral) run ends and the second is the values.
   ```



##########
cpp/src/arrow/c/bridge_test.cc:
##########
@@ -443,6 +444,13 @@ TEST_F(TestSchemaExport, Union) {
              {ARROW_FLAG_NULLABLE});
 }
 
+TEST_F(TestSchemaExport, RunEndEncoded) {
+  TestNested(run_end_encoded(int16(), uint8()), {"+r", "s", "C"},
+             {"", "run_ends", "values"}, {ARROW_FLAG_NULLABLE, 0, ARROW_FLAG_NULLABLE});
+  TestNested(run_end_encoded(int64(), int32()), {"+r", "l", "i"},

Review Comment:
   Just to prove it's not a problem, I'd like to see a test or two where the values are non-primitive (IE nested and/or dictionary encoded)



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