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]

Reporter: Zhuo Peng / @brills
Assignee: Wes McKinney / @wesm

Related issues:

• [C++] C++ array kernels framework and execution buildout (umbrella issue) (relates to)
• [C++] Add "list_size" function that returns Int32Array/Int64Array giving list cell sizes (relates to)
• [C++] Implement "list_parent_indices" vector function (relates to)
• [Python] Expose BinaryArray::total_values_length in bindings (relates to)
• [C++] Add BinaryArray::total_values_length() (relates to)

PRs and other links:

• GitHub Pull Request #7632

_{Note: This issue was originally created as ARROW-6775. Please see the migration documentation for further details.}