[R] Retrieving x argument name from a trellis object in R 2.8.0

[Deepayan Sarkar]

On 11/11/08, vincenzo.2.di-iorio at gsk.com <vincenzo.2.di-iorio at gsk.com> wrote:
> Dear all,
>
>  let consider the following function:
>
>  Fun1 <- function() {
>   library(lattice)
>   plot1 <- 1:10~1:10
>   pl1 <- xyplot(plot1)
>   return(pl1$call$x)
>  }
>
>  In R 2.5.0 (or older version) we have
>
>  > Fun1()
>  plot1
>
>  but starting from R 2.5.1 until the latest R 2.8.0  we obtain instead
>
>  > Fun1()
>  NULL
>
>  because pl1$call seems to be equal to xyplot() without arguments.
>
>  Something like xyplot(x=plot1) doesn?t work either. Again we have that
>  pl1$call is equal to xyplot() without arguments
>
>  The situation is slightly different if we call the xyplot in the global
>  environment:
>
>  > plot1 <- 1:10~1:10
>  > pl1 <- xyplot(plot1)
>  > pl2 <- xyplot(x=plot1)
>
>  then we have
>
>  > pl1$call
>  xyplot(plot1)
>  > pl1$call$x
>  NULL
>
>  but at least
>
>  > pl2$call
>  xyplot(x = plot1)
>  > pl2$call$x
>  plot1

This is what I would have expected.

I'm surprised at the odd behaviour when xyplot() is called inside a
function, which is probably caused by my lack of understanding of how
sys.call() works. However, the 'call' component is provided mainly for
cosmetic reasons, and was never intended to be used programmatically.
Why do you need this?

-Deepayan

>  Someone knows if in R 2.8.0 it is possible to retrieve the name of the x
>  argument (i.e. plot1) directly from an object of class ?trellis? when the
>  corresponding lattice function (e.g. xyplot) is inside another function
>  (e.g. Fun1)?
>
>  Thanks in advance
>  Vincenzo
>
>  -----------------------------------------------------------------------------------
>  Vincenzo Luca Di Iorio
>  Consultant PME User support - GSK R&D Limited
>  -----------------------------------------------------------------------------------
>
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