GroupBy pandas DataFrame and select most common value

Question

I have a data frame with three string columns. I know that the only one value in the 3rd column is valid for every combination of the first two. To clean the data I have to

Answer 1

For agg, the lambba function gets a Series, which does not have a 'Short name' attribute.

stats.mode returns a tuple of two arrays, so you have to take the first element of the first array in this tuple.

With these two simple changements:

source.groupby(['Country','City']).agg(lambda x: stats.mode(x)[0][0])

returns

                         Short name
Country City                       
Russia  Sankt-Petersburg        Spb
USA     New-York                 NY