Dear Steven, > length(x)
> Does this cover all your use > cases? Yes, and thanks again to everybody else who later replied. I had falsely imagined something so much more complicated...!? Next time, I will wait 8*runif(1) before posting. :-) Best, Jay > HTH > > Steven McKinney > > Statistician > Molecular Oncology and Breast Cancer Program > British Columbia Cancer Research Centre > > email: smckinney +at+ bccrc +dot+ ca > > tel: 604-675-8000 x7561 > > BCCRC > Molecular Oncology > 675 West 10th Ave, Floor 4 > Vancouver B.C. > V5Z 1L3 > Canada > > > > > -----Original Message----- > From: [EMAIL PROTECTED] on behalf of G. Jay Kerns > Sent: Mon 11/24/2008 9:41 AM > To: r-help@r-project.org > Subject: [R] how to test for the empty set > > Dear R-help, > > I first thought that the empty set (for a vector) would be NULL. > > x <- c() > x > > However, the documentation seems to make clear that there _many_ empty > sets depending on the vector's mode, namely, numeric(0), character(0), > logical(0), etc. This is borne out by > > y <- letters[1:3] > z <- letters[4:6] > intersect(y,z) > > which, of course, is non-NULL: > > is.null(character(0)) # FALSE > > So, how can we test if a vector is, say, character(0)? The following > doesn't (seem to) work: > > x <- character(0) > x == character(0) # logical(0) > > More snooping led to the following: > > wiki.r-project.org/rwiki/doku.php?id=tips:surprises:emptysetfuncs > > and at the bottom of the page it says "logical(0) is an empty set, > thus is TRUE". However, I get > > isTRUE(logical(0)) # FALSE > > but, on the other hand, > > all.equal(x, character(0)) # TRUE > > This would seem to be the solution, but am I missing something? and in > particular, is there an elegant way to check in the case that the mode > of the vector is not already known? > > Thanks in advance for any insight you may have. > > Best, > Jay > > > > > *************************************************** > G. Jay Kerns, Ph.D. > Associate Professor > Department of Mathematics & Statistics > Youngstown State University > Youngstown, OH 44555-0002 USA > Office: 1035 Cushwa Hall > Phone: (330) 941-3310 Office (voice mail) > -3302 Department > -3170 FAX > E-mail: [EMAIL PROTECTED] > http://www.cc.ysu.edu/~gjkerns/ > > ______________________________________________ > 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. > > -- *************************************************** G. Jay Kerns, Ph.D. Associate Professor Department of Mathematics & Statistics Youngstown State University Youngstown, OH 44555-0002 USA Office: 1035 Cushwa Hall Phone: (330) 941-3310 Office (voice mail) -3302 Department -3170 FAX E-mail: [EMAIL PROTECTED] http://www.cc.ysu.edu/~gjkerns/ ______________________________________________ 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.
