[R] Hook into Coercion Framework for data.frame

[Erich Neuwirth]

statconnDCOM, availagble from rcom.univie.ac.at
is a (D)COM server accessing R.
rcom (available from CRAN) is an R package
which can turn R into a COM server or into a COM client.

These tools have their own mailing list which can
be subscribed at rcom.univie.ac.at.




On 4/26/2011 6:20 PM, Von Der Hirschheydt, Juergen wrote:
> Hi,
> 
> I am looking into a way to hook into the R coercion framework to allow
> me to convert table-like data stored within a COM object into a
> data.frame.
> 
> Some of our COM objects have their own table-like data storage, and from
> R's point of view it's an object (EXTPTRSXP) decoarated with a sepcial
> symbol so we can easily identify it.
> 
> 	COM_Table <- a_method_that_creates_the_object()
> 	class(COM_TABLE)
> 	> "QS.IpdgRelation"
> 
> In addition, we have a method that transforms this object into a
> data.frame:
> 
> 	relation.to.data.frame <- function(obj) { ... }
> 
> A user can easily transform the above object into a data.frame by
> calling:
> 
> 	myDataFrame <- relation.to.data.frame(COM_Table)
> 
> That all works nice and well, but we'd like to take it a step further
> and be able to call
> 
> 	data.frame(COM_Table)		and/or
> 	as.data.frame(COM_Table)
> 
> To achieve the same coercion. I've tried to hook into the coercion by
> using setAs :
> 
> 	setOldClass ( "QS.IpdgRelation" )
> 	setAs ( "QS.IpdgRelation", "data.frame", function(from)
> relation.to.data.frame(from) )
> 
> Which allows me to do
> 
> 	as ( COM_Table, "data.frame" )
> 
> But I can't seem to get the last step to hook this coercion into the
> data.frame() or as.data.frame() call. Is there a way to achieve this, or
> am I chasing a red hering here ?
> 
> Any help appreciated,
> Thanks a lot,
> 
> Juergen
> 
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