conditional sums for pandas aggregate

Question

I just recently made the switch from R to python and have been having some trouble getting used to data frames again as opposed to using R\'s data.table. The problem I\'ve b

Answer 1

To complement unutbu's answer, here's an approach using apply on the groupby object.

>>> df.groupby('A_id').apply(lambda x: pd.Series(dict(
    sum_up=(x.B == 'up').sum(),
    sum_down=(x.B == 'down').sum(),
    over_200_up=((x.B == 'up') & (x.C > 200)).sum()
)))
      over_200_up  sum_down  sum_up
A_id                               
a1              0         0       1
a2              0         1       0
a3              1         0       2
a4              0         0       0
a5              0         0       0