[R] obtaining first and last record for rows with same identifier

[Berton Gunter]

I think by() is simpler:

 by(yourframe,factor(yourframe$patid),function(x)x[c(1,nrow(x)),])



-- Bert Gunter
Genentech Non-Clinical Statistics
South San Francisco, CA
 
"The business of the statistician is to catalyze the scientific learning
process."  - George E. P. Box
 
 

> -----Original Message-----
> From: r-help-bounces at stat.math.ethz.ch 
> [mailto:r-help-bounces at stat.math.ethz.ch] On Behalf Of Sean Davis
> Sent: Tuesday, May 24, 2005 11:38 AM
> To: sms13+ at pitt.edu
> Cc: rhelp
> Subject: Re: [R] obtaining first and last record for rows 
> with same identifier
> 
> If you have your data.frame ordered by the patid, you can use the 
> function rle in combination with cumsum.  As a vector example:
> 
>  > a <- rep(c('a','b','c'),10)
>  > a
>   [1] "a" "b" "c" "a" "b" "c" "a" "b" "c" "a" "b" "c" "a" "b" "c" "a" 
> "b" "c" "a"
> [20] "b" "c" "a" "b" "c" "a" "b" "c" "a" "b" "c"
>  > b <- a[order(a)]
>  > b
>   [1] "a" "a" "a" "a" "a" "a" "a" "a" "a" "a" "b" "b" "b" "b" "b" "b" 
> "b" "b" "b"
> [20] "b" "c" "c" "c" "c" "c" "c" "c" "c" "c" "c"
>  > l <- rle(b)$length
>  > cbind(l,cumsum(l),cumsum(l)-l+1)
>        l
> [1,] 10 10  1
> [2,] 10 20 11
> [3,] 10 30 21
> 
> # use the line below to get the length of the block of the dataframe, 
> the start, and then end indices
>  > cbind(l,cumsum(l)-l+1,cumsum(l))
>        l
> [1,] 10  1 10
> [2,] 10 11 20
> [3,] 10 21 30
>  >
> 
> Sean
> 
> 
> On May 24, 2005, at 2:27 PM, sms13+ at pitt.edu wrote:
> 
> > I have a dataframe that contains fields such as patid, labdate, 
> > labvalue.
> > The same patid may show up in multiple rows because of lab 
> > measurements on multiple days.  Is there a simple way to 
> obtain just 
> > the first and last record for each patient, or do I need to 
> write some 
> > code that performs that.
> >
> > Thanks,
> > Steven
> >
> > ______________________________________________
> > R-help at stat.math.ethz.ch mailing list
> > https://stat.ethz.ch/mailman/listinfo/r-help
> > PLEASE do read the posting guide! 
> > http://www.R-project.org/posting-guide.html
> 
> ______________________________________________
> R-help at stat.math.ethz.ch mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide! 
> http://www.R-project.org/posting-guide.html
>