?tapply ?with is also useful here
as in (untested) with(yourdataframe, tapply(lastpk, id, unique)) -- Bert On Wed, May 2, 2012 at 7:58 AM, Ayyappa Chaturvedula <ayyapp...@gmail.com> wrote: > Dear Group, > > I am working with a large dataset where I need to select for each unique id > the the unique lastpk row. Here is a sample subject: > > id wtdt wt lastpk > > 64050256 2010-09-18 275 2010-09-16 > > 64050256 2010-09-19 277 2010-09-18 > > 64050256 2010-09-20 272 2010-09-18 > > 64050256 2010-09-21 277 2010-09-18 > > > > I want the result as: > > id wtdt wt lastpk > > 64050256 2010-09-18 275 2010-09-16 > > 64050256 2010-09-19 277 2010-09-18 > > > > I am using !(duplicated(data$id)) to select the first row but now I want to > select the first row of the unique lastpk in each unique id. > > > > I appreciate your help on this. > > > > Regards, > > Ayyappa > > [[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. -- Bert Gunter Genentech Nonclinical Biostatistics Internal Contact Info: Phone: 467-7374 Website: http://pharmadevelopment.roche.com/index/pdb/pdb-functional-groups/pdb-biostatistics/pdb-ncb-home.htm ______________________________________________ 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.