Hi Alexander --
On 03/15/2012 07:57 AM, Alexander wrote:
Hi,
I would like to create some S4 classes as follows
setClass("Father",representation(name="character"))
setClass("Son1",contains="Father",representation(par="numeric"))
setClass("Son2",contains="Father",representation(par="logical"))
Son1<-new("Son1")
Son1@name<-"Son1"
Son1@par<-3
it's more efficient to call new("Son1", name="Son1", par=3)
Son2<-new("Son2")
Son2@name<-"Son2"
Son2@par<-TRUE
setGeneric("get.par",function(object){standardGeneric ("get.par")})
functions with '.' in their names can be confusing, because it could
represent an S3 generic on 'get', for an S3 object of class 'par'.
setMethod("get.par","Son1",function(object){return(object@par+3)})
setMethod("get.par","Son2",function(object){return(!object@par)})
get.par(Son1)
get.par(Son2)
So far, so good. I would like now, to create a new class, which
"extends"/"contains" the subclasses of Father by some additional slots.
Is there any clean and simple possibility to inherite also the corresponding
function get.par ?
setClass("Extension",representation(person="Father",text="character"))
Ext<-new("Extension")
Ext@text<-"new try"
Ext@person<-Son1
get.par(Ext)
get.par(Ext@person)
Of course, "get.par(Ext)" returns an error. Is there any possibility to tell
R, that if now function exists for a Class, to transform the object to a
class, for which the function exists ? (I know, it is not very clear what I
am writing, but I am doing my best). I don't want to rewrite every method
for "Extension" like
setMethod("get.par","Extension",function(object){get.par(object@person)})
Is there any simpler solution by steClassUnion, setAs, setIs .... ?
You can provide an explicit relationship
setIs("Extension", "Father",
coerce=function(from) from@person,
replace=function(from, value) {
from@person <- value
from
})
and then define a method on 'Father' (since that's what you're asserting
equivalence to)
setMethod("get.par", "Father", function(object) object@name)
and finally have success with
ext <- new("Extension",
person=new("Son1", name="Son1", par=3),
text="new try")
> get.par(ext)
[1] "Son1"
Neat, eh? But it really pays to ask whether the complexity of the class
structure you're creating is appropriate for the solution that you need
to implement -- imagine, for instance, writing a method that dispatches
on two arguments, and as a programmer you need to implement appropriate
methods for the tangle of dispatch that you have created.
Martin
Thanks a lot in advance
Alexander
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