[R] the first and last observation for each subject

[Carlos J. Gil Bellosta]

Hello,

Is is truly

y=max(y)-min(y)

what you want below?

Best regards,

Carlos J. Gil Bellosta
http://www.datanalytics.com


On Fri, 2009-01-02 at 13:16 -0500, Stavros Macrakis wrote:
> I think there's a pretty simple solution here, though probably not the
> most efficient:
> 
> t(sapply(split(a,a$ID),
>     function(q) with(q,c(ID=unique(ID),x=unique(x),y=max(y)-min(y)))))
> 
> Using 'unique' instead of min or [[1]] has the advantage that if x is
> in fact not time-invariant, this gives an error rather than silently
> ignore inconsistencies.
> 
> Trying to package up this idiom into a function leads to:
> 
> select <-
>   function(df, groupby, selection)
>    {
>      pf <- parent.frame()
>      fields <- substitute(selection)
>      t(sapply(split(df,eval(substitute(groupby),df,enclos=pf)),
>              function(q) eval(fields,q,enclos=pf)))  }
> 
> which I admit is rather ugly (and does no error-checking), but it does work:
> 
> > select(a,ID,list(min(ID),unique(x),max(y)-min(y)))
>     [,1] [,2] [,3]
>   1 1    10   20
>   2 2    12   15
>   3 3    5    5
> 
> Perhaps some of the more experienced people on the list could show me
> how to write this more cleanly.
> 
>            -s
> 
> 
> On Fri, Jan 2, 2009 at 4:20 AM, gallon li <gallon.li at 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]]
> >
> > ______________________________________________
> > R-help at r-project.org mailing list
> > https://stat.ethz.ch/mailman/listinfo/r-help
> > PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
> > and provide commented, minimal, self-contained, reproducible code.
> >
> 
> ______________________________________________
> R-help at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.