Pandas: fill in NaN values with dictionary references another column

Question

I have a dictionary that looks like this

dict = {\'b\' : \'5\', \'c\' : \'4\'}

My dataframe looks something like this

   A  B
0          


        

Answer 1

This can be done simply

df['B'] = df['B'].fillna(df['A'].apply(lambda x: dict.get(x)))

This can work effectively for a bigger dataset as well.