dangotbanned commented on issue #48349:
URL: https://github.com/apache/arrow/issues/48349#issuecomment-3617144584
> pandas needs this for efficient .list[-1] operations with pyarrow-backed
arrays. Currently, pandas must use slow Python loops as a workaround.
For this specific case, you can do:
```py
import pyarrow as pa
import pyarrow.compute as pc
arr = pa.array([[1, 2, 3], [4, 5], [6, 7, 8, 9]])
parent_indices = arr.value_parent_indices()
# NOTE: or `np.arange` if `pyarrow<21`
value_indices = pa.arange(0, len(parent_indices), 1)
# NOTE: These are the defaults, but you can preserve nulls by changing this
options = pc.ScalarAggregateOptions(skip_nulls=True, min_count=1)
grouped_last = (
pa.Table.from_arrays([parent_indices, value_indices], ["parent",
"value"])
.group_by("parent", use_threads=False)
.aggregate([("value", "hash_last", options)])
)
arr.values.take(grouped_last.column(1)).to_pylist()
```
```py
[3, 5, 9]
```
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