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GroupBy nth ignores observed keyword for Categorical #26385

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WillAyd opened this issue May 14, 2019 · 1 comment
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GroupBy nth ignores observed keyword for Categorical #26385

WillAyd opened this issue May 14, 2019 · 1 comment

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@WillAyd
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@WillAyd WillAyd commented May 14, 2019

Was looking to consolidate nth, first and last in the GroupBy world but was hitting some issues with categorical tests and handling of missing data. Note that the following calls are not equivalent, though they should be:

>>> import numpy as np
>>> import pandas as pd

>>> s1 = pd.Categorical([np.nan, 'a', np.nan, 'a'], categories=['a', 'b', 'c'])
>>> s2 = pd.Series([1, 2, 3, 4])
>>> df = pd.DataFrame({'s1': s1, 's2': s2})
>>> grp = df.groupby('s1', observed=False)
>>> grp.first()
     s2
s1
a   2.0
b   NaN
c   NaN

>>> grp.nth(0)
    s2
s1
a    2
@shantanu-gontia
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@shantanu-gontia shantanu-gontia commented May 14, 2019

I get the output -

>>> grp.nth(0)
     s2
s1    
a    2
c    1

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@jreback jreback removed this from the Contributions Welcome milestone Jul 25, 2019
@jreback jreback added this to the 0.25.1 milestone Jul 25, 2019
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3 participants