Thanks a lot for your explanation, which I higly appreciate. But I have still a problem...
Think about 2 persons, each of them create their own package. Both define a generic function "setType" with different arguments. Person 1: setType(obj, valX) Person 2: setType(spec) If I require the package of person 1, everything works fine. If I call the second package afterwards, I will get an error, because the generic function already exists. How can I solve this conflict? How can I define a new generic function which has different arguments without getting in trouble with the first package? Is there a way to define functions, which belongs to a specific class without getting in troubles with other packages? Thanks a lot for your help. Dominik -----Ursprüngliche Nachricht----- Von: Martin Morgan [mailto:[EMAIL PROTECTED] Gesendet: Montag, 25. Februar 2008 19:54 An: Dominik Locher Betreff: Re: AW: [R] Generic Functions Things are different in R. You can't protect a new function from hiding your function, just as > print(1:10) [1] 1 2 3 4 5 6 7 8 9 10 > print <- function(x) "oops" > print(1:10) [1] "oops" > rm(print) > print(1:10) [1] 1 2 3 4 5 6 7 8 9 10 Note that the redefinition hides but does not remove 'print' function. Generics don't really belong with classes, but if you think about it something like class Foo { function bar() {} } foo = new Foo; $foo->bar() in php is very similar to > setClass("Foo", "list") > setGeneric("bar", function(x) standardGeneric("bar")) setMethod("bar", > "Foo", function(x) {}) foo = new("Foo") > bar(foo) i.e., set a method on the generic function. Someone could write another method 'bar' operating on a different object, and it would coexist with your method. Martin "Dominik Locher" <[EMAIL PROTECTED]> writes: > Hi > > Many thanks for your explanation. Just another short question. How can > I make sure that if I greate a new class with functions, that nobody > can change this functions anymore or as you mentioned overwrite > unintended this function (setType). > > In OOP i.e. in php I have a class and specific functions belongs to > this class. How can I do the same in R with generic functions? or is > there another way? > > Thanks for your help. > > Dominik > > > PS: I will send questions about S4 to R-devel@r-project.org in future. ;-). > > -----Ursprüngliche Nachricht----- > Von: Martin Morgan [mailto:[EMAIL PROTECTED] > Gesendet: Sonntag, 24. Februar 2008 17:59 > An: Dominik Locher > Cc: [EMAIL PROTECTED] > Betreff: Re: [R] Generic Functions > > See the 'useAsDefault' argument to setGeneric. > > As an aside, if 'setType<-' is meant to be a 'setter' to change the > value of a slot 'type', then I find the syntax a little redundant -- > it's use > > > setType(x) <- "foo" > > implies that it is already a 'setter' without 'set' at the front. Why > not just > > > type(x) <- "foo" > > (though perhaps 'type' is not such a good name, either)? > > As a second aside, if you're writing code that you expect to be used > with fPortfolio, then having two functions with the same name but > different signatures or overall goals will confuse your user -- with > fPortfolio, > setType<- works fine, but then for mysterious reasons (i.e., when your > package is loaded, with a different definition of setType<-) code that > worked before no longer works! So I'd either use setType in a way > consistent with it's use in fPortfolio, or define a new generic for > your own purposes > (setType<- is not a generic in my version of fPortfolio, > > > packageDescription('fPortfolio')$Version > [1] "260.72" > > ). > > As a third aside, I think questions about S4 probably belong on > R-devel, as they seem to fall in the realm of 'questions likely to > prompt discussion unintelligible to non-programmers' (from the R-devel > mailing list description). > > Martin > > Dominik Locher wrote: >> Hi >> >> I have some problems in defining new generic functions and classes. >> Just have a look at the following example: >> >> >> require(fPortfolio) >> >> setClass("PROBECLASS", >> representation( >> type="character" >> ) >> ) >> >> isGeneric("setType<-") >> #Returns >> TRUE >> >> #I would like to define a specific function for class PROBECLASS with >> other arguments than for the generic function "setType" of fPortfolio. >> setGeneric("setType<-", function(object, value) >> standardGeneric("setType<-")) >> >> #Returns >> Fehler in makeGeneric(name, fdef, fdeflt, group = group, valueClass = >> valueClass, : >> the formal arguments of the generic function for "setType<-" >> (object, >> value) differ from those of the non-generic to be used as the default >> (spec, >> value) >> >> setReplaceMethod("setType", "PROBECLASS", function(object, value){ >> >> [EMAIL PROTECTED] <- value >> object >> >> }) >> >> #Example >> obj = new("PROBECLASS") >> setType(obj) = "test" >> obj >> >> >> ###### >> If I don't require fPortfolio it works fine. However, is it not >> possible to create two generic functions with the same name but >> different > arguments? >> setType for fPortfolio may be differ completely from setType of >> PROBECLASS... >> What's the best way to have functions which belongs to an object of a >> specific class? I had a look at the paper "S4 Classes in 15 pages, >> more or less" (feb12, 2003), however, I could not found what I did > wrong... >> >> Any help is highly appreciated. >> >> Thanks >> Dominik >> >> ______________________________________________ >> [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 >> and provide commented, minimal, self-contained, reproducible code. > -- Martin Morgan Computational Biology / Fred Hutchinson Cancer Research Center 1100 Fairview Ave. N. PO Box 19024 Seattle, WA 98109 Location: Arnold Building M2 B169 Phone: (206) 667-2793 ______________________________________________ R-devel@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-devel
