human
How to sum the nlargest() integers in groupby
assistant
Here is some code to sum the 3 largest integers in groupby by 'STNAME' and 'COUNTY_POP'

df.groupby('STNAME')['COUNTY_POP'].agg(lambda x: x.nlargest(3).sum())

#Warning: this code generation is experimental. Please inspect the code for any bugs before executing.