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...@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@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@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@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.
