Closed
Description
Compare the output of these three groupby/apply calls:
In [66]: df = pd.DataFrame({'a': [1, 1, 2, 2], 'b': range(4)})
In [67]: df
Out[67]:
a b
0 1 0
1 1 1
2 2 2
3 2 3
In [68]: df.groupby('a')['b'].apply(lambda x: 2 * x)
Out[68]:
0 0
1 2
2 4
3 6
dtype: int64
In [69]: df.groupby('a').apply(lambda x: 2 * x)['b']
Out[69]:
0 0
1 2
2 4
3 6
Name: b, dtype: int64
In [70]: df.groupby('a').apply(lambda x: 2 * x['b'])
Out[70]:
a
1 0 0
1 2
2 2 4
3 6
Name: b, dtype: int64
The first two are what I expected; the last is not -- I expected the same result as the previous two.