[R] Access to conditioning variables (lattice)

[William Dunlap]

> -----Original Message-----
> From: r-help-bounces at r-project.org 
> [mailto:r-help-bounces at r-project.org] On Behalf Of Martin D. Lepage
> Sent: Thursday, September 24, 2009 7:38 AM
> To: r-help at r-project.org
> Subject: [R] Access to conditioning variables (lattice)
> 
> [using R version 2.8.1 (2008-12-22)]
> 
> Hello,
> 
> I'm trying to access the conditioning variables of an xyplot within a
> 'panel' function but I have not been able to figure out how to do so.
> Here is a simple example that describes what I wish to do (the problem
> lies with the commented line):
> 
> dataset <- data.frame(x = c(1,2), y = c(4,5), Type = 
> factor(c("a","b")))
> xyplot( y ~ x | Type, dataset, 
>         panel = function(...) {
>             panel.xyplot(...)
> #           do_something_with(conditioning_variables[which.packet()])
>         })
> 
> The problem I am facing is that I do not know how to 
> generically access
> the conditioning variables within the panel function. In this simple
> case, I can achieve what I want to do with the following call :
> 
>     do_something_with(Type[which.packet()])

If your panel function has an argument called 'subscripts' then
xyplot will pass it the row numbers of the data argument that
correspond this the current panel.   E.g.,

   > xyplot( y ~ x | Type, dataset, 
   +         panel = function(..., subscripts) {
   +             panel.xyplot(...)
   +             cat("subscripts=", deparse(subscripts), ":\n")
   +             print(dataset[subscripts,])
   +         })
   subscripts= 1L :
      x y Type
   1 1 4    a
   subscripts= 2L :
      x y Type
   2 2 5    b
You can use that information to add panel-specific information
to the plot.

Bill Dunlap
TIBCO Software Inc - Spotfire Division
wdunlap tibco.com  


> 
> but that requires the panel function call to have prior 
> knowledge of the
> object used as the conditioning variable, which is not flexible enough
> for my needs.
> 
> Thank you,
> Martin D. Lepage
> 
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