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https://issues.apache.org/jira/browse/ARROW-6775?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17147019#comment-17147019
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Wes McKinney commented on ARROW-6775:
-------------------------------------
#3 can be computed using a combination of the {{is_null}} function and Cast, so
I think this is done
{code}
In [1]: arr = pa.array([1, 2, 3, None, None, 6, 7, None])
In [2]: arr.is_null()
Out[2]:
<pyarrow.lib.BooleanArray object at 0x7f783a397e88>
[
false,
false,
false,
true,
true,
false,
false,
true
]
In [3]: arr.is_null().cast('uint8')
Out[3]:
<pyarrow.lib.UInt8Array object at 0x7f7839cb6f48>
[
0,
0,
0,
1,
1,
0,
0,
1
]
{code}
#1 and #4 will need patches. #1 is pretty easy so I'll write a patch for that
soon hopefully
> [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
> Assignee: Wes McKinney
> 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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