Ok, thanks for clarifying. > -----Original Message----- > From: Prof Brian Ripley [mailto:[EMAIL PROTECTED] > Sent: 02 May 2006 12:51 > To: Matthew Dowle > Cc: 'r-help@stat.math.ethz.ch' > Subject: RE: [R] "a"+"b" > > > On Tue, 2 May 2006, Matthew Dowle wrote: > > > Thanks for the information. By 'not easily' it sounds like it is > > possible, but how? > > Change the C code. R is Open Source, so anything is possible. > > > I'm happy to allow 'errors' like "2"+"3"="23", is that what an > > erroneous use could be? > > 2 + x, for example, where x is not numeric. > > > I tried the following, given the info in your reply, which > works. But > > is there a way to allow "a"+"b"="ab"? > >> x = "a" > >> `+.character` <- function(e1, e2) paste(e1,e2, sep="") > >> attr(x,"class")="character" > >> x+x > > [1] "aa" > >> > > > >> -----Original Message----- > >> From: Prof Brian Ripley [mailto:[EMAIL PROTECTED] > >> Sent: 02 May 2006 12:03 > >> To: Matthew Dowle > >> Cc: 'r-help@stat.math.ethz.ch' > >> Subject: Re: [R] "a"+"b" > >> > >> > >> Not easily. There's a comment in ?Ops that for efficiency > the group > >> generics only dispatch on objects with a "class" > attribute: otherwise > >> you could use an S3 method like > >> > >> `+.character` <- function(e1, e2) paste(e1,e2, sep="") > >> > >> S4 methods are built on top of S3 methods as far as > internal dispatch > >> is concerned, so the same comment will apply there AFAICS. > >> > >> I would think that the intention was also to positively discourage > >> messing with the basics of R, as if you were able to do this > >> erroneous uses would > >> likely not get caught. > >> > >> On Tue, 2 May 2006, Matthew Dowle wrote: > >> > >>> > >>> Hi, > >>> > >>> Is there a way to define "+" so that "a"+"b" returns "ab" ? > >>> > >>>> setMethod("+",c("character","character"),paste) > >>> Error in setMethod("+", c("character", "character"), paste) : > >>> the method for function '+' and signature e1="character", > >>> e2="character" is sealed and cannot be re-defined > >>>> "a"+"b" > >>> Error in "a" + "b" : non-numeric argument to binary operator > >>> > >>> Thanks! > >>> > >>> > >>> > >>> [[alternative HTML version deleted]] > >>> > >>> ______________________________________________ > >>> R-help@stat.math.ethz.ch mailing list > >>> https://stat.ethz.ch/mailman/listinfo/r-help > >>> PLEASE do read the posting guide! > >>> http://www.R-project.org/posting-guide.html > >>> > >> > >> -- > >> Brian D. Ripley, [EMAIL PROTECTED] > >> Professor of Applied Statistics, > http://www.stats.ox.ac.uk/~ripley/ > >> University of Oxford, Tel: +44 1865 272861 (self) > >> 1 South Parks Road, +44 1865 272866 (PA) > >> Oxford OX1 3TG, UK Fax: +44 1865 272595 > >> > > > > > > -- > Brian D. Ripley, [EMAIL PROTECTED] > Professor of Applied Statistics, http://www.stats.ox.ac.uk/~ripley/ > University of Oxford, Tel: +44 1865 272861 (self) > 1 South Parks Road, +44 1865 272866 (PA) > Oxford OX1 3TG, UK Fax: +44 1865 272595 >
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