Панды заполняют Na значением из другого столбца
df['Cat1'].fillna(df['Cat2'])
macarrony00
df['Cat1'].fillna(df['Cat2'])df['column'] = df['column'].fillna(0)# based on another column value
df['column_1'].fillna(df['column_2'], inplace=True)# selecting your desired columns
df[['a', 'b']] = df[['a', 'b']].fillna(df['c'], inplace=True)