[R] data frame select max group by like function

[William Dunlap]

And yet another way is
  > isLastInRun <- function(x)c(x[-1]!=x[-length(x)], TRUE)
  > sortedDat <- dat[order(dat$ID,dat$score),]
  > sortedDat[isLastInRun(sortedDat$ID),]
      ID year score
  5 mary 1998   100
  2 rick 1994    90
  1  tom 1995    88
The row names (5,2,1) show where in the
original dataset the output rows
come from.

Bill Dunlap
Spotfire, TIBCO Software
wdunlap tibco.com

> -----Original Message-----
> From: r-help-bounces at r-project.org 
> [mailto:r-help-bounces at r-project.org] On Behalf Of Phil Spector
> Sent: Tuesday, March 09, 2010 11:55 AM
> To: Tan, Richard
> Cc: r-help at r-project.org
> Subject: Re: [R] data frame select max group by like function
> 
> 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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> >
> 
> ______________________________________________
> R-help at r-project.org mailing list
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> PLEASE do read the posting guide 
> http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
>