Propagate values in a multi index dataframe when index value does not exist

Question

I have a multi-index dataframe resulting from a groupby() as follows:

df_grouped = df.groupby(['date', 'name']).agg({'ABC': 'sum'})
df_grouped
                   ABC
date        name 
01-03-2018  Adam   1
            John   2
01-04-2018  Adam   4
            Sam    1
01-05-2018  Adam   5
            John   3
            Sam    2
01-06-2018  Jake   1

I want to propagate the ABC values forward in date only if the name does not exist in the new date. If it exists, then it should be left as it is:

                   ABC
date        name 
01-03-2018  Adam   1
            John   2
01-04-2018  Adam   4
            John   2
            Sam    1
01-05-2018  Adam   5
            John   3
            Sam    2
01-06-2018  Jake   1
            Adam   5
            John   3
            Sam    2

I am not sure how to do this efficiently without looping over each date. Is there a better way, please?

Answer 1

df = df_grouped.unstack().ffill().stack().astype(int)
                 ABC
date       name     
01-03-2018 Adam    1
           John    2
01-04-2018 Adam    4
           John    2
           Sam     1
01-05-2018 Adam    5
           John    3
           Sam     2
01-06-2018 Adam    5
           Jake    1
           John    3
           Sam     2