[ Python 常見問題 ] Pandas - aggregate count distinct (pandas.Series.nunique)

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Question
Let's say I have a log of user activity and I want to generate a report of total duration and the number of unique users per day:

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1. import numpy as np  
2. import pandas as pd  
3.   
4. df = pd.DataFrame({'date': ['2013-04-01','2013-04-01','2013-04-01','2013-04-02', '2013-04-02'],  
5.     'user_id': ['0001', '0001', '0002', '0002', '0002'],  
6.     'duration': [30, 15, 20, 15, 30]})  

Aggregating duration is pretty straightforward:


What I'd like to do is sum the duration and count distinct at the same time, but I can't seem to find an equivalent for count_distinct:

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1. agg_sum_dist_df = group.aggregate({ 'duration': np.sum, 'user_id': count_distinct})  

Below works, but surely there's a better way, no?


HowTo
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