BUG/TST: verify that groupby apply with a column aggregation does not return the column

[jreback]

related #7000

In [1]:  df = DataFrame({'foo1' : ['one', 'two', 'two', 'three', 'one', 'two'],
                                      'foo2' : np.random.randn(6)})

In [2]: df
Out[2]: 
    foo1      foo2
0    one  1.006666
1    two  0.002063
2    two  1.507785
3  three  1.865921
4    one  0.141202
5    two -1.079792

[6 rows x 2 columns]

In [3]: df.groupby('foo1').mean()
Out[3]: 
           foo2
foo1           
one    0.573934
three  1.865921
two    0.143352

[3 rows x 1 columns]

In [4]: df.groupby('foo1').apply(lambda x: x.mean())
Out[4]: 
           foo2
foo1           
one    0.573934
three  1.865921
two    0.143352

[3 rows x 1 columns]

This should return the foo1 column as well

[6]: df.groupby('foo1',as_index=False).apply(lambda x: x.mean())
Out[6]: 
       foo2
0  0.573934
1  1.865921
2  0.143352

[3 rows x 1 columns]

In [7]: df.groupby('foo1',as_index=False).mean()
Out[7]: 
    foo1      foo2
0    one  0.573934
1  three  1.865921
2    two  0.143352

[3 rows x 2 columns]

[jonathanlb]

Extending the example to
df.groupby('foo1').apply(lambda x: x.sum())
produces a DataFrame with column foo1 values oneone three twotwotwo

Should that behavior be preserved?

[OmerJog]

Should that behavior be preserved?

Why not?

[drburrow]

If nobody is currently working on this, I'd like to look more into it.

[fangchenli]

I guess this could be closed.

df = pd.DataFrame({'foo1': ['one', 'two', 'two', 'three', 'one', 'two'],
  ...:                    'foo2': np.random.randn(6)})

df
Out[4]: 
    foo1      foo2
0    one  0.404196
1    two -0.484634
2    two  1.033869
3  three -0.368001
4    one -2.506380
5    two  0.807768

df.groupby('foo1',as_index=False).apply(lambda x: x.mean())
Out[5]: 
    foo1      foo2
0    one -1.051092
1  three -0.368001
2    two  0.452334

df.groupby('foo1',as_index=False).mean()
Out[6]: 
    foo1      foo2
0    one -1.051092
1  three -0.368001
2    two  0.452334

[jreback]

this was recently patched and we should have a test for it

if you like to check (otherwise a PR with this test case would be ok)

[fangchenli]

Sorry for this many commits... It was my first PR.