[FEA] Support groupby collect agg on struct columns

[ayushdg]

Is your feature request related to a problem? Please describe.
Ability to create a list of struct columns using the collect agg via groupby

Describe the solution you'd like

df = cudf.DataFrame(
    {
        'a':['aa','aa','cc'],
        'd':[{"b": '1', "c": "one"}, {"b": '2', "c": "two"}, {"b": '3', "c": "one"}]
     }
)

df.groupby('a').collect()

	d
a	
aa	[{'b': '1', 'c': 'one'}, {'b': '2', 'c': 'two'}]
cc	[{'b': '3', 'c': 'one'}]

Describe alternatives you've considered
N/A

Additional context
Add any other context, code examples, or references to existing implementations about the feature request here.

[quasiben]

I thought this is already supported:

In [3]: df = cudf.DataFrame(
   ...:     {
   ...:         'a':['aa','aa','cc'],
   ...:         'd':[{"b": '1', "c": "one"}, {"b": '2', "c": "two"}, {"b": '3', "c": "one"}]
   ...:      }
   ...: )

In [4]: df.groupby('a').collect()
   ...:
Out[4]:
                                                   d
a
aa  [{'0': '1', '1': 'one'}, {'0': '2', '1': 'two'}]
cc                          [{'0': '3', '1': 'one'}]

[ayushdg]

Based on the discussion in #8474 it seems like it was not supported but working anyway which was resolved in #8499

[quasiben]

Are you ok if we close ?

[ayushdg]

@quasiben Sorry for not clarifying further. The resolution in #8499 was disallowing aggregations on Struct Columns, so this is no longer supported.

[beckernick]

It sounds like this was disallowed because it was erroneously going down a codepath meant for string aggregations (and thus potentially brittle when used with structs/lists).

@ayushdg is the expectation that these operations would behave as before, but by going down a well-tested codepath?

[ayushdg]

@ayushdg is the expectation that these operations would behave as before, but by going down a well-tested codepath?

Yup, that's the expectation.

[shwina]

cc: @vyasr (just FYI), as I think we disabled these aggs on struct columns on one of your groupby cleanup PRs

[vyasr]

Perhaps you're thinking of these changes on #7731? Prior to this, there were a number of dtypes for which unsupported aggregations weren't being checked.

[github-actions]

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