[R] "a"+"b"

[Matthew Dowle]

Ok, thanks for clarifying.

> -----Original Message-----
> From: Prof Brian Ripley [mailto:ripley at stats.ox.ac.uk] 
> Sent: 02 May 2006 12:51
> To: Matthew Dowle
> Cc: 'r-help at 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:ripley at stats.ox.ac.uk]
> >> Sent: 02 May 2006 12:03
> >> To: Matthew Dowle
> >> Cc: 'r-help at 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]]
> >>>
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> >>
> >> --
> >> Brian D. Ripley,                  ripley at stats.ox.ac.uk
> >> 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,                  ripley at stats.ox.ac.uk
> 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
>