[jira] [Created] (ARROW-12942) [C++] The result of Arrow compute hash_min_max is incorrect if there are new groups in the subsequent chunks

["Chenxi Li (Jira)" <ji...@apache.org>]

Chenxi Li created ARROW-12942:
---------------------------------

             Summary: [C++] The result of Arrow compute hash_min_max is incorrect if there are new groups in the subsequent chunks
                 Key: ARROW-12942
                 URL: https://issues.apache.org/jira/browse/ARROW-12942
             Project: Apache Arrow
          Issue Type: Bug
    Affects Versions: 4.0.1, 4.0.0
            Reporter: Chenxi Li
            Assignee: Chenxi Li


If there are new groups in the subsequent chunks of a chunked array, the result of Arrow compute hash_min_max is incorrect.
For example, a table with two chunks, the second chunk has a new group key
{code:java}
First chunk: {"argument": 1, "key": 0},
Second chunk: {"argument": 0,  "key": 1}
{code}
the result of hash_min_max by "key" with such data is
{code:java}
[{"min": null, "max": null}, 0],
[{"min": 0, "max": 0}, 1]
{code}
But it should be 
{code:java}
[{"min": 1, "max": 1}, 0],
[{"min": 0, "max": 0}, 1]
{code}



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