thanks, everyone. I did not even know about transform() and with(), but they look quite useful.
actually, what I had intended to state was that Boolean variables in select parts of subset statements, especially when mixed with other variables that are just part of the data frame, leads to unexpected results. (my d statement was intended to show how easy it is to forget that a variable is not part of the data frame, but just part of the global environment.) unless this mixed-treatment covers an important functional aspect, this might be better to cause a warning (or an error) than a silent recycling of variables. (Related: The recycling rules are generally convenient, but can also be rather problematic in catching errors. It would be nice to be able to turn them off.) regards, /iaw On Tue, Aug 24, 2010 at 3:55 AM, Gavin Simpson <gavin.simp...@ucl.ac.uk> wrote: > On Mon, 2010-08-23 at 17:51 -0400, ivo welch wrote: >> quizz---what does this produce? > > Henrique has provided an answer to the question, but... > >> d=data.frame( a=1:1000, b=2001:3000, z= 5001:6000 ) >> attach(d); c <- (a+b)>25; detach(d) > > ...this is ugly and will potentially catch you out one day if you forget > to detach. These three calls can be achieved using a single with() : > > c <- with(d, (a + b) > 25) > > And the version you wanted: > > attach(d); d$c <- (a+b)>25; detach(d) > > can be done using within(): > > d <- within(d, c <- (a + b) > 25) > > and with the latter, the intention is pretty clear. > > HTH > > G > >> d= subset(d, TRUE, select=c( a, b, c )) >> >> yes, I know I have made a mistake, in that the code does not do what I >> presumably would have wanted. it does seem like unexpected behavior, >> though, without an error. there probably is some reason why this does >> not ring an alarm bell... >> >> /iaw >> ---- >> Ivo Welch (ivo.we...@brown.edu, ivo.we...@gmail.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. > > -- > %~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~% > Dr. Gavin Simpson [t] +44 (0)20 7679 0522 > ECRC, UCL Geography, [f] +44 (0)20 7679 0565 > Pearson Building, [e] gavin.simpsonATNOSPAMucl.ac.uk > Gower Street, London [w] http://www.ucl.ac.uk/~ucfagls/ > UK. WC1E 6BT. [w] http://www.freshwaters.org.uk > %~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~% > > ______________________________________________ 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.
