On 24-Nov-08 17:41:25, G. Jay Kerns wrote: > 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
In the above (and below) cases, would not (length(x)==0) do? Ted. > 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 -------------------------------------------------------------------- E-Mail: (Ted Harding) <[EMAIL PROTECTED]> Fax-to-email: +44 (0)870 094 0861 Date: 24-Nov-08 Time: 18:15:31 ------------------------------ XFMail ------------------------------ ______________________________________________ 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.
