If DF is your data.frame:

subset(cbind(DF, baseline=rep(DF$Y[DF$time == 0], table(DF$ID))), time > 0)

On Tue, Sep 16, 2008 at 11:01 AM, john james <dntssa@yahoo.com> wrote:

> Dear R-help mailing list,
>
> Kindly help me out with this problem:
>
> I have a dataset that is in the format below,
> ID  time  Y  Age
> 1  0     195  23.1
> 1  2    204  23.3
> 1  4   202    23.5
> 2  0  170    22.0
> 2  3   234   22.2
> 3  0  208   24.4
> 3  2  194  24 .7
> 3  3   204  24.9
>
> I wish to remove all the measurements at time point 0 and convert them to a
> baseline variable as follows;
>
>  ID  time  Y  Age  baseline
> 1  2    204  23.3   195
> 1  4   202    23.5   195
> 2  3   234   22.2    170
> 3  2  194  24 .7     208
> 3  3   204  24.9     208
>
> Thanks.
>
> regards
> John
>
>
>
>
>
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>
>
> ______________________________________________
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> PLEASE do read the posting guide
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> and provide commented, minimal, self-contained, reproducible code.
>
>


-- 
Henrique Dallazuanna
Curitiba-Paraná-Brasil
25° 25' 40" S 49° 16' 22" O

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