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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