[R] How to suppress plotting for "xyplot(zoo(x))"?

[Marius Hofert]

Hi,

I found the thread http://r.789695.n4.nabble.com/Matrix-as-input-to-xyplot-lattice-proper-extended-formula-syntax-td896948.html 
I used Gabor's approach and then tried to assign the plot to a variable (see below). But a Quartz device is opened... why? I don't want to have anything plot/printed, I just would like to store the plot object. Is there something like "plot = FALSE"?

Cheers,

Marius

library(lattice)
library(zoo)

df <- data.frame(y = matrix(rnorm(24), nrow = 6), x = 1:6) 
xyplot(zoo(df[1:4], df$x), type = "p")

plot.object <- xyplot(zoo(df[1:4], df$x), type = "p") # problem: a Quartz device is opened (on Mac OS X 10.6)