operation between columns according to the value it contains

I have a Dataframe that look like this:

df_1:

    Phase_1  Phase_2   Phase_3
0      8       4        2
1      4       6        3
2      8       8        3
3      10      5        8
...

I’d like to add a column called "Coeff" that compute (Phase_max - Phase_min) / Phase_max

For the first row: Coeff= (Phase_1 – Phase_3)/ Phase_1 = (8-2)/8 = 0.75

Expected OUTPUT:

df_1

    Phase_1  Phase_2   Phase_3   Coeff
0      8       4        2       0.75
1      4       6        3       0.5
2      8       8        3       0.625
3      10      5        8       0.5

What is the best way to compute this without using loop? I want to apply it on large dataset.

>Solution :

here is one way to do it

# list the columns, you like to use in calculations
cols=['Phase_1', 'Phase_2', 'Phase_3']

# using max and min across the axis to calculate, for the defined columns

df['coeff']=(df[cols].max(axis=1).sub(df[cols].min(axis=1))).div(df[cols].max(axis=1))
df
df

    Phase_1     Phase_2     Phase_3     coeff
0         8           4           2     0.750
1         4           6           3     0.500
2         8           8           3     0.625
3         10          5           8     0.500