[R] par(new = TRUE) - overplotting

[Antje]

Hi everybody,

I want to create some boxplots (as png) within an lapply method. To get nice 
gridlines behind the boxplot, I plotted it twice and therefore I set par(new=TRUE).
This works nicely for the first plot but the second does plot on the first plot 
too and creates a mess...
How can I force to start with a blank plot again???

lapply(c(1,2), FUN=function(i) {
	png(filename = "test.png", width = 450, height = 600)
	gridlines <- seq(0.1,2.0,0.1)
	par(mar=c(12, 4, 5, 2))
	bpars <- list(yaxt = "n", las = 2 )
	boxplot(mydata[i], pars= bpars )
	abline(h = gridlines, col="lightgray", lty=2)
	abline(h = 1, col="red", lwd=3)
	par(new=TRUE)
	boxplot(mydata[i], pars= bpars, main = "title")
	dev.off()
})

Ciao,
Antje