Re: [R] "a"+"b"

From: Matthew Dowle <mdowle_at_concordiafunds.com>
Date: Tue 02 May 2006 - 21:41:47 EST

Thanks for the information. By 'not easily' it sounds like it is possible, but how? I'm happy to allow 'errors' like "2"+"3"="23", is that what an erroneous use could be?

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@stats.ox.ac.uk]
> 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]]
> >
> > ______________________________________________
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> >
>
> --
> Brian D. Ripley, ripley@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
>



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