Dear Gallon,
Assuming that your data is called "mydata", something like this should do
the job:
newdf<-data.frame(
ID = unique(mydata$ID),
x = unique(mydata$x),
y = with(mydata,tapply(y,ID,function(m) tail(m,1)-head(m,1)))
)
newdf
HTH,
Jorge
On Fri, Jan 2, 2009 at 4:20 AM, gallon li <gallon...@gmail.com> wrote:
> I have the following data
>
> ID x y time
> 1 10 20 0
> 1 10 30 1
> 1 10 40 2
> 2 12 23 0
> 2 12 25 1
> 2 12 28 2
> 2 12 38 3
> 3 5 10 0
> 3 5 15 2
> .....
>
> x is time invariant, ID is the subject id number, y is changing over time.
>
> I want to find out the difference between the first and last observed y
> value for each subject and get a table like
>
> ID x y
> 1 10 20
> 2 12 15
> 3 5 5
> ......
>
> Is there any easy way to generate the data set?
>
> [[alternative HTML version deleted]]
>
> ______________________________________________
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> PLEASE do read the posting guide
> http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
>
[[alternative HTML version deleted]]
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