On 28/10/2014, 5:32 AM, Martin Maechler wrote: > Diverted to R-devel, as I'm requesting comments about a proposal > to add is.whole() to R just so this issue does not trail on for > centuries (;-), see below. >
I didn't read the thread in question, but I think Bill's comment is crucial: what properties of integers are you interested in testing? One that comes up a lot is that some non-integral values print as integers, and people get confused when using them as indices. For example, this prints results that surprise some people: x <- 1:10 index <- 4 - 1.e-10 index x[index] I would think is.whole(index) should return FALSE here, but the sfsmisc function defaults to a nonzero tolerance, and returns TRUE. Duncan Murdoch >>>>>> William Dunlap <wdun...@tibco.com> >>>>>> on Sat, 18 Oct 2014 10:33:05 -0700 writes: > > > 3. all.equal(a, as.integer(a)) > > Note that this one tests if 'a' can be stored accurately as a 32-bit > signed > > integer. If you want to know if 'a' can be used as an accurate count, > then > > you want to test if a+1>a (use abs() in case a is negative). E.g., try > this > > for a<-2^49-1, about 5*10^14. > > > You have to decide what properties of integers you are interested in. > > > Bill Dunlap > > TIBCO Software > > wdunlap tibco.com > > good point, thank you, Bill. > > This whole issue comes up about once year (at least), it seems to me, > and every time there are some good and some not so good propositions, > some aiming for vectorized / whole object solutions some, only > assuming scalar input. > > Indeed, I'd claim that all three proposals cited below are not > good enough in one way or the other.... though one > could argue that a "tolerance = 0" version would be good enough, > and hence the > function(x) x %% 1 == 0 > would be sufficient. > > In the CRAN package 'sfsmisc' (which I maintain), Alain Hauser > recently added an > > is.whole() > > function which works "vectorized" and uses a 'tolerance' and > then all.equal(), but in better way than (most / all ?) what was proposed in > this thread (line 486 ff of > https://github.com/mmaechler/sfsmisc/blob/master/R/misc-goodies.R ). > > Further, the CRAN packages > 'gmp' ("infinite" precision integer and rational arithmetic) and > 'Rmpfr' ('infinite' precision floating point arithmetic) contain > an S3 generic is.whole() function and methods for their own > number classes and a default method (( which "however" assumes > a tolerance of zero, the same as the x %% 1 == 0 proposal)). > > Given all this, the r-help and stackoverflow threads, > maybe we should decide that such an is.whole() function should > be added to R and maintained (by me for the time), so we do have > a better place to point people to, and well documented -- and > eventually "optimized" -- behavior ? > > Personally I do think I'd want a "signature" of > function (x, tolerance = sqrt(.Machine$double.eps)) > > > Martin > > > > On Sat, Oct 18, 2014 at 10:02 AM, PO SU <rhelpmaill...@163.com> wrote: > >> > >> Tks for your help, after investigate in your link, i find there seems > three ways can be adoped: > >> 1. is.wholenumber <- function(x, tol = .Machine$double.eps^0.5) > abs(x - round(x)) < tol) > >> e.g. is.wholenumber(1) > >> 2. x%%1==0 > >> > >> > >> 3. all.equal(a, as.integer(a)) > >> > >> > >> and also included your last suggestion using floor. and also tks for > other helpers！ > >> -- > >> > >> PO SU > >> mail: desolato...@163.com > >> Majored in Statistics from SJTU > >> > >> At 2014-10-18 22:48:15, "Sergio Fonda" <sergio.fond...@gmail.com> > wrote: > >> > >> Sorry for my previous hurry misunderstanding. > >> Try this link: > >> > http://stackoverflow.com/questions/3476782/how-to-check-if-the-number-is-integer > >> > >> 2014-10-18 16:25 GMT+02:00 PO SU <rhelpmaill...@163.com>: > >> > >> It's due to that, 1 is a numeric, 1.2 is a numeric, though it's true. > but deeply, when i want to know 1 is an integer, there seems no easy way to > get the answer. > >> > >> So, is there anyone happen to know it? > >> > > >> > >> At 2014-10-18 20:10:09, "S Ellison" <s.elli...@lgcgroup.com> wrote: > >> > >>>> But i use a<-10/b , b is some value ,may be 5, maybe 5.5 > >> > >>> If you do floating point arithmetic on integers you'll usually get > floating point answers, including the 5.0. > >> > >>> > >> > >>> See FAQ 7.31 for the usual floating point problem, and ?all.equal for > the usual answer to it. You could see if a result is close to an integer > by,for example, using all.equal to compare it to itself after rounding. > >> > >>> > >> > >>> S > > ______________________________________________ > R-devel@r-project.org mailing list > https://stat.ethz.ch/mailman/listinfo/r-devel > ______________________________________________ R-devel@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-devel
