[jira] [Created] (ARROW-9249) [C++] Implement "list_parent_indices" vector function

["Wes McKinney (Jira)" <ji...@apache.org>]

Wes McKinney created ARROW-9249:
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             Summary: [C++] Implement "list_parent_indices" vector function 
                 Key: ARROW-9249
                 URL: https://issues.apache.org/jira/browse/ARROW-9249
             Project: Apache Arrow
          Issue Type: New Feature
          Components: C++
            Reporter: Wes McKinney
             Fix For: 1.0.0


The return value has the same size as the child array of a List type and contains values providing the "cell index" of each child value relative to the parent list array.

For example, the list array

{code}
[ [0, 1], null, [2], [3, 4]]
{code}

would output

{code}
[0, 0, 2, 3, 3]
{code}

Note that there is no null because the child array has no nulls. If the list has null values whose offsets point to non-empty child sections then these will have to be null in the output to preserve the contract that the output array has the same length as the child array



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