[R-sig-Epi] question about selecting observations

[FZ]

This is not really an epi question.  Also, please read the posting guide 
which tells you to provide a reproducible example.

Anyhow, I think this may do what you want:

datasorted <- data[order(data$ID, data$date, decreasing=TRUE),]

firstobs<- data[!duplicated(data$Date),]

This assumes that by first observation you mean the first record for 
each Date. You can easily extend this to select the first observation by ID.

I hope this helps,

Francisco

Lynn Disney wrote:
> I have a large dataset and I need to sort by ID and date, then select
> the first observation...I have seen how to do this and delete the first
> obs. Not sure how to extend the concept...
> 
>  
> 
> Can anyone help?
> 
>  
> 
> Lynn D. Disney, Ph.D., J.D., M.P.H.
> 
> Research Analyst
> 
> SEIU 1199
> 
> 1771 E. 30th Street
> 
> Cleveland, Ohio 44114
> 
> Telephone: (216) 566-0117
> 
> Email: ldisney at seiu1199.org <mailto:ldisney at seiu1199.org> 
> 
> 
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