[R] "a"+"b"

[Matthew Dowle]

Perfect. Thank you!

> -----Original Message-----
> From: Martin Morgan [mailto:mtmorgan at fhcrc.org] 
> Sent: 02 May 2006 17:10
> To: Matthew Dowle
> Cc: 'Prof Brian Ripley'; "'r-help@/usr/bin/idn: 
> idna_to_ascii_4z() failed with error 3. 
> <r-help at stat.math.ethz.ch>"@fhcrc.org
> Subject: Re: [R] "a"+"b"
> 
> 
> I think %any-symbol% defines a binary operator, so
> 
> > "%+%" <- function(x,y) paste(x,y,sep="")
> > "a" %+% "b"
> [1] "ab"
> > 
> 
> or for more fun
> 
> > setGeneric("%+%", function(x,y) standardGeneric("%+%"))
> [1] "%+%"
> > setMethod("%+%", signature(x="character", y="character"), 
> > function(x,y) paste(x,y,sep=""))
> [1] "%+%"
> > setMethod("%+%", signature(x="numeric", y="numeric"), function(x,y) 
> > x+y)
> [1] "%+%"
> > "a" %+% "b"
> [1] "ab"
> > 1 %+% 2
> [1] 3
>  
> 
> Martin
> 
> Matthew Dowle <mdowle at concordiafunds.com> writes:
> 
> > 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 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
> >>
> >
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