sohailshk opened a new issue, #41305:
URL: https://github.com/apache/beam/issues/41305

   ### What happened?
   
   The proxy of `DeferredGroupBy.skew()` is computed by pandas on an empty 
frame, where the integer or bool dtype of the input is kept, while the real 
result for such columns is float64. Converting the result with `to_pcollection` 
infers an integer schema, and encoding the rows then fails. Example (default 
runner):
   
       import apache_beam as beam
       from apache_beam.dataframe.convert import to_dataframe, to_pcollection
   
       rows = [beam.Row(a=i + 1, c=c) for i, c in enumerate('xyxyxzzx')]
       with beam.Pipeline() as p:
           df = to_dataframe(p | beam.Create(rows))
           to_pcollection(df.groupby('c').skew(), include_indexes=True) | 
beam.Reshuffle()
   
   With Beam 2.77.0 from PyPI this fails with `ValueError: Attempted to encode 
null for non-nullable field "a"`, and with master from source with `TypeError: 
unsupported operand type(s) for &: 'float' and 'int'`. The proxy dtype of `a` 
is int64, the real dtype float64 (NaN for the groups with fewer than 3 rows). 
`SeriesGroupBy.skew()` has the same wrong proxy dtype. Expected: a float64 
proxy for integer and bool columns, as for `groupby().mean()`. I plan to cast 
those proxy columns to float64.
   
   Version: 2.77.0, and master at 2a7c56bacb1.
   
   ### Issue Priority
   
   Priority: 2 (default / most bugs should be filed as P2)
   
   ### Issue Components
   
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