[R] par(new=T) with xyplot

[Paul Murrell]

Hi


> I know I should not mix base plotting functions with grid/lattice functions,
> but I have used a "quick-and-dirty" trick of par(new=T) in the past for
> annotating a trellis-drawn graph in various versions of S-PLUS.  The
> sequence goes something like this:
> 
> > windows(width = 5, height = 5, pointsize = 10)  # open up the device
> 
> > xyplot(y ~ x)
> > par(new=T)
> > xyplot(y2 ~ x)
> > par(new=F)
> 
> Using R 1.5.0 in Windows, I tried this for the first time today, and the
> par(new=T) setting appears to be ignored by the second xyplot call; i.e.,
> the frame is cleaned and only the second printing of xyplot appears on the
> device.  (If instead of the second xyplot I use a base plot function like
> plot.default, the frame is not cleaned, which I want to happen).
> 
> Is there anything analogous to par(new=T) that I could use to achieve this
> behavior of "not cleaning the frame" with lattice commands? Any workaround
> or advice is appreciated.


You can use the "more" argument to the print.trellis() function.  For
example, ...

library(lattice)
x <- rnorm(10)
y <- rnorm(10)
y2 <- rep(0, 10)
p1 <- xyplot(y ~ x, ylim=c(-5, 5)) 
p2 <- xyplot(y2 ~ x, pch=16, ylim=c(-5, 5), ylab=" ")
print.trellis(p1, more=TRUE)
bg <- trellis.par.get("background")
bg$col <- "transparent"
trellis.par.set("background", bg)
print.trellis(p2)

... NOTE the need to set the background to "transparent" before doing
the second plot.

Hope that helps

Paul
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