Pandas Fill NA with Group Value

Question

Given the following data frame:

import pandas as pd
import numpy as np
df = pd.DataFrame({\'Site\':[\'A\',\'A\',\'A\',\'B\',\'B\',\'B\',\'C\',\'C\',\'C\'],
          


        

Answer 1

You can use transform as answered here

df['Value'] = df.groupby('Site').transform(lambda x: x.fillna(x.mean()))


  Site  Value
0    A      1
1    A      1
2    A      1
3    B      2
4    B      2
5    B      2
6    C      3
7    C      3
8    C      3