That should be:
transform(DF, Time = ave(1:nrow(DF), Subject, FUN = function(ix) with(DF[ix,], if (any(Marker == 1)) Time - Time[Marker == 1] else Time))) On Fri, Dec 4, 2009 at 6:36 PM, Gabor Grothendieck <ggrothendi...@gmail.com>wrote: > Try this: > > transform(DF, Time = ave(1:nrow(DF), Subject, FUN = function(ix) > if (any(Marker[ix] == 1)) Time - Time[Marker == 1] else Time)) > > > > > On Fri, Dec 4, 2009 at 5:47 PM, Dennis Fisher <fis...@plessthan.com>wrote: > >> Colleagues, >> >> R 2.9.0 on all platforms >> >> I have a dataset that contains three columns of interest: ID's, serial >> elapsed times, and a marker. Representative data: >> Subject Time Marker >> 1 100.5 0 >> 1 101 0 >> 1 102 1 >> 1 103 0 >> 1 105 0 >> >> For each subject, I would like to find the time associated with MARKER == >> 1, then replace Time with Time - (Time[Marker == 1]) >> The result for this subject would be: >> Subject Time Marker >> 1 -1.5 0 >> 1 -1 0 >> 1 0 1 >> 1 1 0 >> 1 3 0 >> >> One proviso: some subjects do not have Marker == 1; for these subjects, I >> would like Time to remain unchanged. >> >> At present, I am looping over each subject. The number of subjects is >> large so this process is quite slow. I assume that one of the apply >> functions could speed this markedly but I am not facile with them. Any help >> would be appreciated. >> >> Dennis >> >> Dennis Fisher MD >> P < (The "P Less Than" Company) >> Phone: 1-866-PLessThan (1-866-753-7784) >> Fax: 1-866-PLessThan (1-866-753-7784) >> www.PLessThan.com >> >> ______________________________________________ >> 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. >> > > [[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.
