If you want to obtain a data frame you can use the functions head and tail
like:
dat=data.frame(id=rep(1:5,3),num=rnorm(15), num2=rnorm(15))#Creates data
frame with id
last=do.call("rbind",by(dat,dat$id,tail,1))#Selects the last observation for
each id
first=do.call("rbind",by(dat,dat$id,head,1))#Selects the first observation
for each id
newdat=rbind(first,last)#Joins data
newdat=newdat[order(newdat$id),]#sorts data by id
Notice that rownames will give you the original row location of the
observations selected
I hope this helps
Francisco
From: Berton Gunter <[EMAIL PROTECTED]>
To: "'Sean Davis'" <[EMAIL PROTECTED]>, <[EMAIL PROTECTED]>
CC: "'rhelp'" <r-help@stat.math.ethz.ch>
Subject: RE: [R] obtaining first and last record for rows with same
identifier
Date: Tue, 24 May 2005 12:17:58 -0700
I think by() is simpler:
by(yourframe,factor(yourframe$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: [EMAIL PROTECTED]
> [mailto:[EMAIL PROTECTED] On Behalf Of Sean Davis
> Sent: Tuesday, May 24, 2005 11:38 AM
> To: [EMAIL PROTECTED]
> 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, [EMAIL PROTECTED] 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
> >
> > ______________________________________________
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>
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