The 'polynom' package provides one example of how to do this.
However, getAnywhere("+.polynomial") just told me "no object named
‘+.polynomial’ was found"; I don't know why. The documentation says it
uses S3 classes. The 'Matrix' package should provide other examples,
using S4 classes. You can get the package source for both as "*.tar.gz"
files from CRAN, unzip the file and see what they did.
Hope this helps.
Spencer
Peter Dalgaard wrote:
hadley wickham wrote:
On Thu, Jul 10, 2008 at 5:09 AM, Peter Dalgaard
<[EMAIL PROTECTED]> wrote:
Tine wrote:
Hi!
I was just wondering is there anyway to overload operator for custom
class.
For example:
I have two matrices A and B with same dimensions. I want to overload
operator '+' with my own function.
Or even better can I create my own (new) operator.
Example:
A+-B where '+-' would be some function.
You can define an S3 method
"+.myclass" <- function(a,b) {...}
Notice that dispatch is only on the 1st argument. This is a generic
weakness of S3 methods. The Matrix package implements similar things
with S4 methods, but it does tend to get rather complicated.
That's not completely true is it?
2 * unit(2, "cm")
[1] 2*2cm
unit(2, "cm") * 2
[1] 2*2cm
(But I'm not sure why that works)
Group generics. Yes, I forgot about those. They dispatch on _any_
argument being of a given class. The problem is that it is a single
dispatch, which is why R gets itself in a twist when you try to add
Dates and difftimes:
as.Date("2008-7-10")+as.difftime(2,units="days")
[1] "2008-07-12"
Warning message:
Incompatible methods ("+.Date", "Ops.difftime") for "+"
as.difftime(2,units="days")+as.Date("2008-7-10")
Time difference of 14072 days
Warning message:
Incompatible methods ("Ops.difftime", "+.Date") for "+"
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