Count distinct in Pandas aggregation

import pandas as pd
import numpy as np

Create a dataframe

#create a dataframe
df = pd.DataFrame({'date': ['2013-04-01','2013-04-01','2013-04-01','2013-04-02', '2013-04-02'],
'user_id': ['0001', '0001', '0002', '0002', '0002'],
'duration': [30, 15, 20, 15, 30]})
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

Count distinct in Pandas aggregation

#here we can count the number of distinct users viewing on a given day
df = df.groupby("date").agg({"duration": np.sum, "user_id": pd.Series.nunique})
df

	duration	user_id
date
2013-04-01	65	2
2013-04-02	45	1