Dear Spencer,
> -----Original Message----- > From: Spencer Graves [mailto:[EMAIL PROTECTED] > Sent: Saturday, December 04, 2004 8:00 PM > To: John Fox > Cc: 'John Chambers'; [EMAIL PROTECTED]; 'Martin Maechler' > Subject: Re: [R] Testing for S4 objects (redux) > > Which version of R? > Sorry -- this was with R 2.0.1 under Windows. John > I just replicated it in R 2.0.0patched. I know that > 2.0.1 is now available, but I haven't found time to upgrade yet. > > By the way, I can replicate the error message with only > one line: > > > getClass("by") > Error in getClass("by") : "by" is not a defined class > > hope this helps. spencer graves > > John Fox wrote: > > >Dear John, > > > >I've encountered the following problem: > > > > > > > >>x <- rnorm(100) > >>y <- sample(2, 100, replace=TRUE) > >>res <- by(x, y, mean) > >>res > >> > >> > >INDICES: 1 > >[1] 0.1129494 > >------------------------------------------------------------ > >INDICES: 2 > >[1] -0.2066684 > > > > > >>isS4object <- function(object)(length(attr(object, "class"))==1 && > >> > >> > >+ !is.null(getClass(class(object)))) > > > > > >>isS4object(res) > >> > >> > >Error in getClass(class(object)) : "by" is not a defined class > > > > > > > >For a simple question, this has gotten rather complicated. Any > >suggestions would be appreciated. > > > >Regards, > > John > > > >-------------------------------- > >John Fox > >Department of Sociology > >McMaster University > >Hamilton, Ontario > >Canada L8S 4M4 > >905-525-9140x23604 > >http://socserv.mcmaster.ca/jfox > >-------------------------------- > > > > > > > >>-----Original Message----- > >>From: John Chambers [mailto:[EMAIL PROTECTED] > >>Sent: Tuesday, November 30, 2004 9:40 AM > >>To: John Fox > >>Cc: Martin Maechler; [EMAIL PROTECTED] > >>Subject: Re: [R] Testing for S4 objects > >> > >>Let me suggest a different test, because slotNames was > written to work > >>differently when given a string or a class definition. With your > >>definition, > >> > >>R> x <- "classRepresentation" > >>R> isS4object(x) > >>[1] TRUE > >> > >>which I assume is not what you wanted. (Given a single string, > >>slotNames() tries to look up the class definition of that name.) > >> > >>How about the following? The logic is that an S4 object > must have an > >>actual class attribute of length 1 (that rules out basic > data types, > >>where class(x) is a string but there is no actual > attribute, and also > >>rules out some S3 objects). Then if that's true, try to > look up the > >>class definition. If it is non-null, seems like an S4 object. > >> > >>R> isS4object <- function(object)(length(attr(object, > "class"))==1 && > >>+ !is.null(getClass(class(object)))) > >>R> isS4object(x) > >>[1] FALSE > >>R> isS4object(getClass(class(x))) > >>[1] TRUE > >> > >>This definition seems to work, at least on the examples I > could think > >>of right away. Notice though, that some classes, such as > "ts", that > >>have been around for a long while are nevertheless legitimate S4 > >>classes, so: > >> > >>R> t1 = ts(1:12) > >>R> isS4object(t1) > >>[1] TRUE > >> > >>(this applies to either version of isS4object). > >> > >>There are a couple of details, more appropriate for the > r-devel list. > >>Seems a good candidate for a function to add to R. > >> > >> > >>On Sat, 27 Nov 2004 17:48:30 -0500, John Fox > <[EMAIL PROTECTED]> wrote: > >> > >> > >>>Dear Martin, > >>> > >>>As it turns out, the test that I proposed (i.e., testing for NULL > >>>slotNames) sometimes fails. For example: > >>> > >>> > >>> > >>>>library(car) > >>>>data(Prestige) > >>>>sum <- summary(lm(prestige ~ income + education, data=Prestige)) > >>>>slotNames(sum) > >>>> > >>>> > >>>character(0) > >>> > >>>The following, however, seems to work (at least as far as > I've been > >>>able to > >>>ascertain): > >>> > >>>isS4object <- function(object) length(slotNames(object)) != 0 > >>> > >>>I hope that this is a more robust test. > >>> > >>> > >>> > >>>John > >>> > >>>-------------------------------- > >>>John Fox > >>>Department of Sociology > >>>McMaster University > >>>Hamilton, Ontario > >>>Canada L8S 4M4 > >>>905-525-9140x23604 > >>>http://socserv.mcmaster.ca/jfox > >>>-------------------------------- > >>> > >>> > >>> > >>>>-----Original Message----- > >>>>From: Martin Maechler [mailto:[EMAIL PROTECTED] > >>>>Sent: Friday, November 26, 2004 3:18 AM > >>>>To: John Fox > >>>>Cc: [EMAIL PROTECTED] > >>>>Subject: Re: [R] Testing for S4 objects > >>>> > >>>> > >>>> > >>>>>>>>>"JohnF" == John Fox <[EMAIL PROTECTED]> > >>>>>>>>> on Thu, 25 Nov 2004 22:28:50 -0500 writes: > >>>>>>>>> > >>>>>>>>> > >>>> JohnF> Dear r-help list members, Is there a way to test > >>>> JohnF> whether an object is an S4 object? The best that I've > >>>> JohnF> been able to come up with is > >>>> > >>>> JohnF> isS4object <- function(object) > >>>>!(is.null(slotNames(object))) > >>>> > >>>>you can drop one pair of "(..)" to give > >>>> > >>>> isS4object <- function(object) !is.null(slotNames(object)) > >>>> > >>>> > >>>> JohnF> which assumes that an S4 object has at least one > >>>> JohnF> slot. I think this is safe, but perhaps I'm missing > >>>> JohnF> something. > >>>> > >>>>The question is a very good one -- that I have posed to R-core a > >>>>while ago myself. > >>>> > >>>>Inside utils:::str.default {which doesn't show the many > >>>> > >>>> > >>commments > >> > >> > >>>>in the *source* of str.default()}, I have wanted a way that even > >>>>works when the 'methods' package is not attached and use the more > >>>>obscure > >>>> > >>>> #NOT yet:if(has.class <- !is.null(cl <- class(object))) > >>>> if(has.class <- !is.null(cl <- attr(object, "class")))# > >>>>S3 or S4 class > >>>> S4 <- !is.null(attr(cl, "package"))## <<<'kludge' FIXME! > >>>> ##or length(methods::getSlots(cl)) > 0 > >>>> > >>>>For the time being, I'd keep your function, but I don't > >>>> > >>>> > >>think we'd > >> > >> > >>>>guarantee that it will remain the appropriate test in all > >>>> > >>>> > >>future. > >> > >> > >>>>But till then many things will have happened (if not all of them > >>>>;-). > >>>> > >>>>Martin Maechler, ETH Zurich > >>>> > >>>> > >>>> > >>>______________________________________________ > >>>[EMAIL PROTECTED] mailing list > >>>https://stat.ethz.ch/mailman/listinfo/r-help > >>>PLEASE do read the posting guide! > >>>http://www.R-project.org/posting-guide.html > >>> > >>> > >>> > > > >______________________________________________ > >[EMAIL PROTECTED] mailing list > >https://stat.ethz.ch/mailman/listinfo/r-help > >PLEASE do read the posting guide! > >http://www.R-project.org/posting-guide.html > > > > > > -- > Spencer Graves, PhD, Senior Development Engineer > O: (408)938-4420; mobile: (408)655-4567 > > ______________________________________________ [EMAIL PROTECTED] mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html
