[R] data frame select max group by like function

[Ista Zahn]

Hi Richard,
There are probably better ways, but here is one approach:

Dat <- read.table(textConnection("ID, year, score
tom, 1995, 88
rick, 1994, 90
mary, 2000, 97
tom, 1998, 60
mary, 1998,100"), header=TRUE, sep=",")

MaxScore <- aggregate(Dat$score, list(Dat$ID), max)
names(MaxScore) <- c("ID", "score")
MaxYear <- merge(Dat, MaxScore)

Best,
Ista


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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>
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-- 
Ista Zahn
Graduate student
University of Rochester
Department of Clinical and Social Psychology
http://yourpsyche.org