Python pandas – filter rows after groupby

You just need to use apply on the groupby object. I modified your example data to make this a little more clear:

import pandas
from io import StringIO

csv = StringIO("""index,A,B
0,1,0.0
1,1,3.0
2,1,6.0
3,2,0.0
4,2,5.0
5,2,7.0""")

df = pandas.read_csv(csv, index_col='index')
groups = df.groupby(by=['A'])
print(groups.apply(lambda g: g[g['B'] == g['B'].max()]))

Which prints:

         A  B
A index      
1 2      1  6
2 4      2  7