how to collapse columns in pandas on null values?

Question

Suppose I have the following dataframe:

pd.DataFrame({\'col1\':    [\"a\", \"a\", np.nan, np.nan, np.nan],
            \'override1\': [\"b\", np.nan, \"b\",          


        

Answer 1

import pandas as pd
import numpy as np
df=pd.DataFrame({'col1':    ["a", "a", np.nan, np.nan, np.nan],
            'override1': ["b", np.nan, "b", np.nan, np.nan],
            'override2': ["c", np.nan, np.nan, "c", np.nan]})

print(df)
df=df['col1'].fillna('') + df['override1'].fillna('')+ df['override2'].fillna('')
print(df)