如果值相同，如何检查 3 列是否相同并添加一个具有该值的新列？

Question

I have a dataframe that look like this..

index   Column A    Column B    Column C
0        alice       alice       alice
1        nick        nick        john
2        juli        nick        alice

I want to check in Column A, Column B and Column C are equal or not. If equal, I want to add the the value as a new Column D . If not, add None to Column D

I did this so far..

def func(row):
    if ((row['Column A']) == (row['Column B']) == (row['Column C'])):
        df['Column D'] = df['Column A']
    else:
        df['Column D'] = None

When I applied the function using.. df.apply (lambda row: func(row),axis =1) , I am not getting the desired output.

I got something like this..

index   Column A    Column B    Column C    Column D
0      alice        alice       alice        None
1      nick         nick        john         None
2      juli         nick        alice        None

whereas, I want the output to be like..

index   Column A    Column B    Column C    Column D
0      alice        alice       alice        alice
1      nick         nick        john         None
2      juli         nick        alice        None

Any help on this?

Answer 1

use numpy where

here you are taking a subset of the dataframe to compare and store to an array arr then comparing the first column of the array against the rest of the columns.

import numpy as np
arr = df[['A','B','C']].values
df['D'] = np.where((arr == arr[:, [0]]).all(axis=1),df['A'],None)

or

def func(row):
    if ((row['A']) == (row['B']) == (row['C'])):
        return row['A']
    else:
        return None

df['D'] = df.apply(lambda row: func(row),axis =1)

Answer 2

In your if clause you wrote:

(row['Column A']) == (row['Column B']) == (row['Column C'])

I'm not sure if it is the right way to do it. Have you tried this code below as your if clause?

((row['Column A']) == (row['Column B'])) and ((row['Column B']) == (row['Column C']))

Answer 3

I tried df['Column D'] = np.where((((df['Column A'])==(df['Column B']))& (df['Column B'] == df['Column C'])),df['Column A'],None)

and this worked! Thanks all for giving the idea.