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https://issues.apache.org/jira/browse/ARROW-15089?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17476066#comment-17476066
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Dhruv Vats commented on ARROW-15089:
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I thought to ask this before I got too confused. Some (possibly very naive)
questions:
* Is {{{}MapArray{}}}, which inherits from {{{}ListArray{}}}, a collection of
individual {{{}MapTypes{}}}, each of which in turn are a like {{{}List [
Struct1 \{key, value}, Struct2 \{key, value}, ... ]{}}}?
* Arrow doesn't restrict the DataType {{key}} takes on, so what is the correct
way to take it as a parameter to a {{{}kernel{}}}.
* Some kernels use {{Call}} while others use {{{}ExecSomething{}}}, what are
the prerequisites/strategies/reasonings behind these?
* If the {{MapArray}} definition in the first point is correct, how do the
{{MapArray.keys/items}} work? Do they return a _combined_ Array of keys/items?
If so, then iterating and checking for matches in this {{keys}} Array is what
we are looking for here?
I'm pretty sure I'm getting a lot of things mixed up. Still finding my way
through the expansive Arrow type system, where each subdirectory is like a
codebase in itself it seems.
> [C++] Add compute kernel to get MapArray value for given key
> ------------------------------------------------------------
>
> Key: ARROW-15089
> URL: https://issues.apache.org/jira/browse/ARROW-15089
> Project: Apache Arrow
> Issue Type: Improvement
> Components: C++
> Affects Versions: 6.0.1
> Reporter: Will Jones
> Assignee: Dhruv Vats
> Priority: Major
> Labels: C++, Kernels, beginner, compute, good-second-issue,
> kernel
>
> Given a "map", an obvious operation is to get an item corresponding to a key.
> The idea here is to create a kernel that does this for each map in the array.
> IIRC MapArray isn't guaranteed to have unique keys. So one version would
> return an array of ItemType by returning the first of last item for a given
> key. Yet another version could return a ListType containing all matching
> items.
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