Joris Van den Bossche created ARROW-15643:
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Summary: [C++] Kernel to select subset of fields of a StructArray
Key: ARROW-15643
URL: https://issues.apache.org/jira/browse/ARROW-15643
Project: Apache Arrow
Issue Type: Improvement
Components: C++
Reporter: Joris Van den Bossche
Triggered by
https://stackoverflow.com/questions/71035754/pyarrow-drop-a-column-in-a-nested-structure.
I thought there was already an issue about this, but don't directly find one.
Assume you have a struct array with some fields:
{code}
>>> arr = pa.StructArray.from_arrays([[1, 2, 3]]*3, names=['a', 'b', 'c'])
>>> arr.type
StructType(struct<a: int64, b: int64, c: int64>)
{code}
We have a kernel to select a single child field:
{code}
>>> pc.struct_field(arr, [0])
<pyarrow.lib.Int64Array object at 0x7ffa9e229940>
[
1,
2,
3
]
{code}
But if you want to subset the StructArray to some of its fields, resulting in a
new StructArray, that's not possible with {{struct_fields}}, and doing this
manually is a bit cumbersome:
{code}
>>> fields = ['a', 'c']
>>> arrays = [arr.field(n) for n in fields]
>>> arr_subset = pa.StructArray.from_arrays(arrays, names=fields)
>>> arr_subset.type
StructType(struct<a: int64, c: int64>)
{code}
(this is still OK, but if you had a ChunkedArray, it certainly gets annoying)
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