Pandas aggregate count distinct

>>> df          date  duration user_id 0  2013-04-01        30    0001 1  2013-04-01        15    0001 2  2013-04-01        20    0002 3  2013-04-02        15    0002 4  2013-04-02        30    0002

>>> df.groupby("date").agg({"duration": np.sum, "user_id": pd.Series.nunique})             duration  user_id date                          2013-04-01        65        2 2013-04-02        45        1

>>> df.groupby("date").agg({"duration": np.sum, "user_id": lambda x: x.nunique()})             duration  user_id date                          2013-04-01        65        2 2013-04-02        45        1