I am trying to divide each row in a column by the maximum of a sub-list in the column where the sub-list if the column filtered by a category variable

Is there a single line vector equation that creates col3? I have been trying to use groupby with transform(lambda x: x...) but can't seem to get the effect of maxif where it only takes the max of col2 where col1 = the rows with the same category as the row in col2 being divided.

Sample input code:

import pandas as pd

data = {'col1':['A', 'A', 'B', 'B'],
        'col2':[1, 2, 3, 4]}

df = pd.DataFrame(data)

df

Desired output:

CodePudding user response：

Sure:

>>> df['col2'] / df.groupby('col1')['col2'].transform(max)
0    0.50
1    1.00
2    0.75
3    1.00

You could then assign that result to a new column of your choice.