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https://issues.apache.org/jira/browse/ARROW-6775?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17114510#comment-17114510
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Wes McKinney commented on ARROW-6775:
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I think these can all be implemented as kernels with the new compute framework
after ARROW-8792. I have linked the issue
> [C++] [Python] Proposal for several Array utility functions
> -----------------------------------------------------------
>
> Key: ARROW-6775
> URL: https://issues.apache.org/jira/browse/ARROW-6775
> Project: Apache Arrow
> Issue Type: Wish
> Components: C++, Python
> Reporter: Zhuo Peng
> Priority: Minor
>
> Hi,
> We developed several utilities that computes / accesses certain properties of
> Arrays and wonder if they make sense to get them into the upstream (into both
> the C++ API and pyarrow) and assuming yes, where is the best place to put
> them?
> Maybe I have overlooked existing APIs that already do the same.. in that case
> please point out.
>
> 1/ ListLengthFromListArray(ListArray&)
> Returns lengths of lists in a ListArray, as a Int32Array (or Int64Array for
> large lists). For example:
> [[1, 2, 3], [], None] => [3, 0, 0] (or [3, 0, None], but we hope the returned
> array can be converted to numpy)
>
> 2/ GetBinaryArrayTotalByteSize(BinaryArray&)
> Returns the total byte size of a BinaryArray (basically offset[len - 1] -
> offset[0]).
> Alternatively, a BinaryArray::Flatten() -> Uint8Array would work.
>
> 3/ GetArrayNullBitmapAsByteArray(Array&)
> Returns the array's null bitmap as a UInt8Array (which can be efficiently
> converted to a bool numpy array)
>
> 4/ GetFlattenedArrayParentIndices(ListArray&)
> Makes a int32 array of the same length as the flattened ListArray.
> returned_array[i] == j means i-th element in the flattened ListArray came
> from j-th list in the ListArray.
> For example [[1,2,3], [], None, [4,5]] => [0, 0, 0, 3, 3]
>
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