[R] Tidiest way of modifying S4 classes?

[Patrick Connolly]

I wish to make modifications to the plot.pedigree function in the
kinship package.  My attempts to contact the maintainer have been
unsuccessful, but my question is general, so specifics of the kinship
package might not be an issue.

My first attempt was to make a new function Plot.pedigree in the
.GlobalEnv which mostly achieved what I wanted to.  However, I'm sure
that's not the tidiest way to do it.  We don't have the green book,
but there's lots of interesting information I found here:

http://www.stat.auckland.ac.nz/S-Workshop/Gentleman/S4Objects

However, there's something I'm missing in connecting that information
into knowledge of how I go about making a new method or slot or
whatever is sensible in this case.  What does one make of this:


> getClass(class(kinship:::plot.pedigree))

No Slots, prototype of class "function"

Extends: "OptionalFunction", "PossibleMethod"

Known Subclasses: 
Class "MethodDefinition", from data part
Class "genericFunction", from data part
Class "functionWithTrace", from data part
Class "derivedDefaultMethod", by class "MethodDefinition"
Class "MethodWithNext", by class "MethodDefinition"
Class "SealedMethodDefinition", by class "MethodDefinition"
Class "standardGeneric", by class "genericFunction"
Class "nonstandardGenericFunction", by class "genericFunction"
Class "groupGenericFunction", by class "genericFunction"
> 


If I want a new plot.pedigree function, do I make a slot, or what is
the approach to take?

Suggestions most welcome.

Thanks

-- 
Patrick Connolly
HortResearch
Mt Albert
Auckland
New Zealand 
Ph: +64-9 815 4200 x 7188
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