[R] overloading + operator for chars
Martin Morgan
mtmorgan at fhcrc.org
Wed Nov 2 21:24:49 CET 2011
On 11/02/2011 06:52 AM, Albert-Jan Roskam wrote:
> Hello,
>
> I would like to overload the "+" operator so that it can be used to concatenate two strings, e.g "John" + "Doe" = "JohnDoe".
> How can I 'unseal' the "+" method?
>> setMethod("+", signature(e1="character", e2="character"), function(e1, e2) paste(e1, e2, sep="") )
> Error in setMethod("+", signature(e1 = "character", e2 = "character"), :
> the method for function "+" and signature e1="character", e2="character" is sealed and cannot be re-defined
>>
>
Hi -- I think the two issues are that "+" is part of the "Arith" group
generic (?Methods, ?Arith) and that `+` (actually, members of the Ops
group) for primitive types dispatches directly without doing method
look-up. Personally I might
setClass("Character", contains="character")
Character <- function(...) new("Character", ...)
setMethod("Arith", c("Character", "Character"), function(e1, e2) {
switch(.Generic,
"+"=Character(paste(e1, e2, sep="")),
stop("unhandled 'Arith' operator '", .Generic, "'"))
})
and then
> Character(c("foo", "bar")) + Character("baz")
[1] "foobaz" "barbaz"
Some might point to
> `%+%` <- function(e1, e2) paste(e1, e2, sep="")
> "foo" %+% "bar"
[1] "foobar"
Martin
> Cheers!!
> Albert-Jan
>
>
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