categorical sorting within date group in dataframe

January 18, 2024

I have a dataframe like this one and would like to make sure to sort it by date and have the
same ordering for side for status emtries, I would like to see B entries on top before S for each date. But also keep the dates where there is only one entry.

tempDF = pd.DataFrame({ 'id': [12,12,12,12,45,45,45,51,51,51,51,51,51,76,76,76],
                'date': ['2015-05-01','2015-05-22','2015-05-14','2015-05-06','2015-05-03','2015-05-12','2015-05-02','2015-05-05','2015-05-01','2015-05-23','2015-05-17','2015-05-03','2015-05-05','2015-05-04','2015-05-22','2015-05-08'],
                'status': ['B','S','B','S','B','B','S','B','S','B','B','S','S','B','B','S']})
tempDF['date'] = pd.to_datetime(tempDF['date'])

I tried

tempDF.sort_values(['status']).groupby(tempDF['date']).head(2)

but this ends up the entries sorted before being grouped

>Solution :

If I understand correctly, first sort_values then grouby.head with sort=False:

(tempDF.sort_values(by=['date', 'status'], ascending=True)
       .groupby('date', sort=False).head(2)
)

Output:

    id       date status
0   12 2015-05-01      B
8   51 2015-05-01      S
6   45 2015-05-02      S
4   45 2015-05-03      B
11  51 2015-05-03      S
13  76 2015-05-04      B
7   51 2015-05-05      B
12  51 2015-05-05      S
3   12 2015-05-06      S
15  76 2015-05-08      S
5   45 2015-05-12      B
2   12 2015-05-14      B
10  51 2015-05-17      B
14  76 2015-05-22      B
1   12 2015-05-22      S
9   51 2015-05-23      B

Similarly, if you want all Bs before all Ss:

tempDF.sort_values(by=['status', 'date'], ascending=True)
       .groupby('date', sort=False).head(2)
)

Output:

    id       date status
0   12 2015-05-01      B
4   45 2015-05-03      B
13  76 2015-05-04      B
7   51 2015-05-05      B
5   45 2015-05-12      B
2   12 2015-05-14      B
10  51 2015-05-17      B
14  76 2015-05-22      B
9   51 2015-05-23      B
8   51 2015-05-01      S
6   45 2015-05-02      S
11  51 2015-05-03      S
12  51 2015-05-05      S
3   12 2015-05-06      S
15  76 2015-05-08      S
1   12 2015-05-22      S