按组识别 pandas 数据帧中的第一个条目

Question

I have data like this

I wish to generate this:

How can I do this using Pandas? I know I need to group by id and order by date somehow... Thanks for your help in advance

Answer 1

In [2]: df = pd.DataFrame({'id' : [1]*3 + [2]*3 + [3],
   ...: 'date' : ['01/02/2020', '02/02/2020', '03/02/2020', '01/02/2020', '02/02/2020', '03/02/2020', '04/05/2020']})
   ...: df
Out[2]: 
   id        date
0   1  01/02/2020
1   1  02/02/2020
2   1  03/02/2020
3   2  01/02/2020
4   2  02/02/2020
5   2  03/02/2020
6   3  04/05/2020

In [3]: df['Entry'] = ''
   ...: df.loc[df.date.isin(df.groupby("id").agg(min).date), 'Entry'] = 'First'
   ...: df
Out[3]: 
   id        date  Entry
0   1  01/02/2020  First
1   1  02/02/2020       
2   1  03/02/2020       
3   2  01/02/2020  First
4   2  02/02/2020       
5   2  03/02/2020       
6   3  04/05/2020  First