[R] Aggregate by First case

[Dimitris Rizopoulos]

try this:

dat <- read.table(textConnection(
"Id         Year
123456 2001
123456 2002
123456 2003
655432 2001
655432 2002
655432 2003"), header = TRUE)
closeAllConnections()

dat[!duplicated(dat$Id), ]
# or
dat[tapply(row.names(dat), dat$Id, head, 1), ]


I hope it helps.

Best,
Dimitris

----
Dimitris Rizopoulos
Biostatistical Centre
School of Public Health
Catholic University of Leuven

Address: Kapucijnenvoer 35, Leuven, Belgium
Tel: +32/(0)16/336899
Fax: +32/(0)16/337015
Web: http://med.kuleuven.be/biostat/
     http://www.student.kuleuven.be/~m0390867/dimitris.htm


----- Original Message ----- 
From: "Jojje Andersson" <dietaamigo at hotmail.com>
To: <r-help at r-project.org>
Sent: Friday, May 30, 2008 9:13 AM
Subject: [R] Aggregate by First case


> Hello!
>
> I have an maybe a to a simple question but I cant get it right.
>
> I have a dataframe with in one column an id-variable and in another 
> a year-variable. One id-number can occur several years.
> I have sorted the dataframe on id then on year so the same id-number 
> is sorted by year with the first occurens at top.
>
> Now I want to make a subset of this dataframe with just the first 
> year the id-number occur, so the first case of every id.
>
> Id         Year
> 123456 2001
> 123456 2002
> 123456 2003
> 655432 2001
> 655432 2002
> 655432 2003
>
> Is there a simple command I can do?
>
> Thanks!
>
> Jojje
>
>
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