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.
