how to get the column name from multiple column into one if its true in pyhton?

Question

i have a data frame

A     B      C    
True  False  False
False False  True
True  False  False
False False  False

I want to get column named “result” which will return the column name if it is true and nan, if any of it is not True.

Expected Column

result
A
C
A  
na

Asked By: Amit

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Source

Answer 1

You could use Series.where to set the column value to either the idxmax along the second axis, so the respective column name of the first True, or NaN, depending on the result of df.any(1) :

df['result'] = df.idxmax(1).where(df.any(1))

Or for a numpy based one you can use argmax instead:

import numpy as np

df['result'] = np.where(df.values.any(1), df.columns[df.values.argmax(1)], np.nan)

print(df)

       A      B      C result
0   True  False  False      A
1  False  False   True      C
2   True  False  False      A
3  False  False  False    NaN

Answered By: yatu

Answer 2

You could simply iterate on the columns in reverse order:

for col in reversed(df.columns):
    df.loc[df[col],'result'] = col

It gives:

       A      B      C result
0   True  False  False      A
1  False  False   True      C
2   True  False  False      A
3  False  False  False    NaN

Answered By: Serge Ballesta

Answer 3

IIUC dot

df.dot(df.columns)
0    A
1    C
2    A
3     
dtype: object

Answered By: BENY

Answer 4

Update pandas 1.5+ pd.from_dummies:

pd.from_dummies(df, default_category='na')

Output:

0   A
1   C
2   A
3  na

Therfore,

df['result'] = pd.from_dummies(df, default_category='na')
df

Output:

       A      B      C result
0   True  False  False      A
1  False  False   True      C
2   True  False  False      A
3  False  False  False     na

Answered By: Scott Boston

how to get the column name from multiple column into one if its true in pyhton?

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