How to apply formula on a column in Dataframe based on value from other column-CodePudding

I have a DataFrame and I want to apply formula on Column A based on Column B.

If Column B has some values then apply formula on column A (100 - column value). Below is the data I have.

DataFrame Input

      A         B 
0     35       TYLER
1     20       MACK
2     30       MACK
3     40       MITCH

If column B has 'MACK' and 'MITCH' then apply formula, else not. How can I do that?

DataFrame Output

       A         B 
0     35       TYLER
1     80       MACK
2     70       MACK
3     60       MITCH

CodePudding user response：

You can limit your formula to just the matching rows with boolean indexing:

apply_rows = df["B"].isin(["MACK", "MITCH"])
df.loc[apply_rows, "A"] = 100 - df.loc[apply_rows, "A"]

CodePudding user response：

You could also use isin mask:

df['A'] = df['A'].mask(df['B'].isin(['MACK','MITCH']), 100-df['A'])

or isin numpy.where

import numpy as np
df['A'] = np.where(df['B'].isin(['MACK','MITCH']), 100-df['A'], df['A'])

Output:

    A      B
0  35  TYLER
1  80   MACK
2  70   MACK
3  60  MITCH