[R] Obtaining the first /or last record of a subject in alongitudinal study

[Daniel Malter]

Had the same problem recently. I used a loop. Assume your data frame is
called "data" and your units of observation are "Subject". 

first.round.index=NULL
final.round.index=NULL
for(i in unique(Subject)){
    first.round.index[i]=min(which(Subject==i))
    final.round.index[i]=max(which(Subject==i))
    }

first.round.index=first.round.index[is.na(first.round.index)==F]
final.round.index=final.round.index[is.na(final.round.index)==F]

##This gives you the row numbers for first, respectively last, observation
for each subject

##Then you can select the data rows of your data according to first- or
final.row.index, e.g.:

data.first.round=data[first.round.index, ]
data.final.round=data[final.round.index, ]


-------------------------
cuncta stricte discussurus
-------------------------

-----Ursprüngliche Nachricht-----
Von: r-help-bounces at r-project.org [mailto:r-help-bounces at r-project.org] Im
Auftrag von Luwis Tapiwa Diya
Gesendet: Thursday, August 07, 2008 6:22 AM
An: R-help at r-project.org
Betreff: [R] Obtaining the first /or last record of a subject in
alongitudinal study

Dear R users,

I was wondering if anyone knows how to obtain(subset) the first and/or the
last record of a subject in a longitudinal setup.

Normally in SAS one uses first.variable1 and last.variable1. So my question
is that is there an R way of doing this.

Regards,

--
Luwis Diya, Phd student (Biostatistics), Biostatistical Center, School Of
Public Health, Catholic University of Leuven, U.Z. St Raphael,
Kapucijnenvoer 35, B-3000 Leuven, Belgium,

Cell: +32(0)497 22 94 83
Phone:+32(0)16 32 68 86 [Office]
Phone:+32(0)16 32 98 76 [Home]
Fax: +32(0)16 33 70 15

Email: luwis.diya at med.kuleuven.be
http://med.kuleuven.be/biostat/staff/LD.htm

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