[R] First. Last. Data row selection

[Nutter, Benjamin]

I've attached some functions I've written based on previous questions
that have been posted here.  Unfortunately, I was too lazy to give
credit to previous commenters in my Rd file, and for that I hope they'll
forgive me.  

In any case, please be assured that the functions I've attached are in
no way my original work.

Benjamin

-----Original Message-----
From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-project.org]
On Behalf Of wookie1976
Sent: Tuesday, February 23, 2010 12:40 PM
To: r-help at r-project.org
Subject: [R] First. Last. Data row selection


I am in the process of switching from SAS over to R.  I am working on
very large CSV datasets that contain vehicle information.  As I am
processing the data, I need to select the first (or sometimes the
second) record (by date) for any records that have the same license
plate number.  In SAS, there is a function called 'first.' that can be
used on sorted datasets to pull out those first entries for each
occurrence of a particular variable  (in this case the variable is
'license plate') found in the data.  I have spent some time looking
around and cannot seem to find an equivalent function in R. 
Can anyone recommend an efficient technique that would pull this off?  I
assume the database must first be sorted by vehicle plate and date, and
then apply the filter or function.  Any help would be greatly
appreciated.  

Thanks, Joe
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