Hi, I have a data frame with 3 columns: ID, year and score.  How can I
select for each unique ID, the year that has the max score?  For
example, for data frame
 
ID, year, score
tom, 1995, 88
rick, 1994, 90
mary, 2000, 97
tom, 1998, 60
mary, 1998,100
 
I shall have
ID, year, score
tom, 1995, 88
rick, 1994, 90
mary, 1998,100
 
Thanks,
Richard

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