Zhuo Peng created ARROW-6775:
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Summary: Proposal for several Array utility functions
Key: ARROW-6775
URL: https://issues.apache.org/jira/browse/ARROW-6775
Project: Apache Arrow
Issue Type: Wish
Reporter: Zhuo Peng
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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