pandas: replace values in column with the last character in the column name

I have a dataframe as follows:

import pandas as pd
df = pd.DataFrame({'sent.1':[0,1,0,1],
                'sent.2':[0,1,1,0],
                'sent.3':[0,0,0,1],
                'sent.4':[1,1,0,1]
               })

I am trying to replace the non-zero values with the 5th character in the column names (which is the numeric part of the column names), so the output should be,

   sent.1  sent.2  sent.3  sent.4
0       0       0       0       4
1       1       2       0       4
2       0       2       0       0
3       1       0       3       4

I have tried the following but it does not work,

print(df.replace(1, pd.Series([i[5] for i in df.columns], [i[5] for i in df.columns])))

However when I replace it with column name, the above code works, so I am not sure which part is wrong.

print(df.replace(1, pd.Series(df.columns,  df.columns)))

>Solution :

Since you’re dealing with 1’s and 0’s, you can actually just use multiply the dataframe by a range:

df = df * range(1, df.shape[1] + 1)

Output:

   sent.1  sent.2  sent.3  sent.4
0       0       0       0       4
1       1       2       0       4
2       0       2       0       0
3       1       0       3       4

Or, if you want to take the numbers from the column names:

df = df * df.columns.str.split('.').str[-1].astype(int)