Groupby #pandas

groupby.py

import pandas as pd

df = pd.DataFrame(
                    {
                      'AAA': [1,1,1,2,2,2,2,3,3],
                      'BBB': [2,1,3,4,5,1,2,3,7]
                    }

                  )
print(df,'\n')

#First group df by the classes in A (1,2,3),then get the index of the minimum number of B in each class of A.
group_min = df.loc[df.groupby('AAA')['BBB'].idxmin()]
print(group_min, '\n')

#sort then take first of each
First_of_each = df.sort_values(by='BBB').groupby('AAA', as_index=False).first()
print(First_of_each)

--------------------------------------------------------------------------------------------------
Output:

   AAA  BBB
0    1    2
1    1    1
2    1    3
3    2    4
4    2    5
5    2    1
6    2    2
7    3    3
8    3    7 

   AAA  BBB
1    1    1
5    2    1
7    3    3 

   AAA  BBB
0    1    1
1    2    1
2    3    3