[Python] Replace every value after the maximum value by 1 in each group

The objective is to assign 1s to any index in the group that is a higher value than the one retrieved from idxmax()

import numpy as np
import pandas as pd
df = pd.DataFrame({'id':[1, 1, 1, 2, 2, 2, 3, 3, 3], 'val':[1,np.NaN, 0, np.NaN, 1, 0, 1, 0, 0]})

id val
0 1 1.0
1 1 NaN
2 1 0.0
3 2 NaN
4 2 1.0
5 2 0.0
6 3 1.0
7 3 0.0
8 3 0.0


We can use idxmax() to get the index values for the highest value in each group

test = df.groupby('id')['val'].idxmax()

id
1 0
2 4
3 6


The objective is to transform the data to look as such (which is that every value in group that has a higher index than the one from idxmax() gets assigned a 1.

id val
0 1 1.0
1 1 1.0
2 1 1.0
3 2 NaN
4 2 1.0
5 2 1.0
6 3 1.0
7 3 1.0
8 3 1.0



This question does not necessarily need to be done with idxmax(). Open to any suggestions.

Continue reading...