[R] data frame select max group by like function

[Phil Spector]

Yet another way to do this with base R:

> dat = read.csv(textConnection('ID, year, score
+ tom, 1995, 88
+ rick, 1994, 90
+ mary, 2000, 97
+ tom, 1998, 60
+ mary, 1998,100'))
> do.call(rbind,lapply(split(dat,dat$ID),function(x)x[which.max(x$score),]))
        ID year score
mary mary 1998   100
rick rick 1994    90
tom   tom 1995    88

 					- Phil Spector
 					 Statistical Computing Facility
 					 Department of Statistics
 					 UC Berkeley
 					 spector at stat.berkeley.edu


On Tue, 9 Mar 2010, Tan, Richard 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
>
> 	[[alternative HTML version deleted]]
>
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