pandas: how to check if a column value is in other columns in the same row

Question

I have a pandas data frame in the following format:

col1 col2 col3 col4 col5
A    A    B    Z    X
B    A    Z    Z    X
A    A    C    Z    X
C    A    C    D    X
D    A    B    D    X

How can I filter the rows where the value in col1 is in col2, col3 or col4 (disregarding col5)?

I tried among other things:

df = df[df[['col2', 'col3', 'col4']].isin(['col1'])]

but get an empty data frame.

The expected output would be:

col1 col2 col3 col4 col5
A    A    B    Z    X
A    A    C    Z    X
C    A    C    D    X
D    A    B    D    X

Answer 1

Check if any of the values are equal (eq) the value in column 1. DataFrame.eq supports an axis argument.

m = df[['col2', 'col3', 'col4']].eq(df['col1'], axis=0).any(1)
df[m]

  col1 col2 col3 col4 col5
0    A    A    B    Z    X
2    A    A    C    Z    X
3    C    A    C    D    X
4    D    A    B    D    X