[jira] [Created] (ARROW-18137) Allow passing no aggregations to TableGroupBy.aggregate

["Jacek Pliszka (Jira)" <ji...@apache.org>]

Jacek Pliszka created ARROW-18137:
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             Summary: Allow passing no aggregations to TableGroupBy.aggregate
                 Key: ARROW-18137
                 URL: https://issues.apache.org/jira/browse/ARROW-18137
             Project: Apache Arrow
          Issue Type: New Feature
          Components: C++, Python
    Affects Versions: 9.0.0
            Reporter: Jacek Pliszka


If we could allow TableGroupBy.aggregate to accept no aggregation functions then it would behave like pandas drop_duplicates.

{code:python}
t.group_by(['keys', 'values']).aggregate()
{code}

I did some naive benchmarks and looks like it should be 30% faster than converting to pandas and deduplicating. This was my naive test:

{code:python}
 t.append_column('i', pa.array([1]*len(t),pa.int64())).group_by(['keys', 'values']).aggregate([("i", "max")]).drop(['i_max'])
{code}

And on small 5M table it took 245ms while 359ms for t.to_pandas().drop_duplicates()

Actual aggregation without adding dummy column should be  even faster still will allow drop_duplicates functionality until better implementation arrives



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