[R] data frame select max group by like function

[Gabor Grothendieck]

Try this.  The aggregate call gives a data frame with the ID and max
score.  Then we merge that back with the original data frame so that
we pick up the year too:

merge(DF, aggregate(DF['score'], DF['ID'], max))

On Tue, Mar 9, 2010 at 1:35 PM, Tan, Richard <RTan at panagora.com> wrote:
> 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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