Many thanks to you both. I have now filed away for future reference the 2 factor tapply as well as the extremely useful looking plyr library. And the code worked beautifully :-)
On 24 Aug 2010, at 19:47, "Abhijit Dasgupta, PhD" <[email protected]> wrote: > The paste-y argument is my usual trick in these situations. I forget that > tapply can take multiple ordering arguments :) > > Abhijit > > On 08/24/2010 02:17 PM, David Winsemius wrote: >> >> On Aug 24, 2010, at 1:59 PM, Abhijit Dasgupta, PhD wrote: >> >>> The only problem with this is that Chris's unique individuals are a >>> combination of Type and ID, as I understand it. So Type=A, ID=1 is a >>> different individual from Type=B,ID=1. So we need to create a unique >>> identifier per person, simplistically by uniqueID=paste(Type, ID, sep=''). >>> Then, using this new identifier, everything follows. >> >> I see your point. I agree that a tapply method should present both factors >> in the indices argument. >> >> > new.df <- txt.df[ -which( txt.df$nn <=1), ] >> > new.df <- new.df[ with(new.df, order(Type, ID) ), ] # and possibly needs >> > to be ordered? >> > new.df$diffdays <- unlist( tapply(new.df$dt2, list(new.df$ID, >> > new.df$Type), function(x) x[1] -x) ) >> > new.df >> Type ID Date Value dt2 nn diffdays >> 1 A 1 16/09/2020 8 2020-09-16 3 0 >> 2 A 1 23/09/2010 9 2010-09-23 3 3646 >> 4 B 1 13/5/2010 6 2010-05-13 3 0 >> >> But do not agree that you need, in this case at least, to create a paste()-y >> index. Agreed, however, such a construction can be useful in other >> situations. >> > > > -- > > Abhijit Dasgupta, PhD > Director and Principal Statistician > ARAASTAT > Ph: 301.385.3067 > E: [email protected] > W: http://www.araastat.com > ______________________________________________ [email protected] 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.
