Printing multiple ggplots into a single pdf, multiple plots per page

Question

I have a list, p, where each element of p is a list of ggplot2 plotting objects.

I would like to output a single pdf containing all the plots in p such that the plots in p[[1]] are on page 1, the plots in p[[2]] are on page 2, etc. How might I do this?

Here's some example code to provide you with the data structure I'm working with--apologies for the boring plots, I picked variables at random.

require(ggplot2) p <- list()  cuts <- unique(diamonds$cut) for(i in 1:length(cuts)){     p[[i]] <- list()     dat <- subset(diamonds, cut==cuts[i])     p[[i]][[1]] <- ggplot(dat, aes(price,table)) + geom_point() +          opts(title=cuts[i])     p[[i]][[2]] <- ggplot(dat, aes(price,depth)) + geom_point() +          opts(title=cuts[i]) } 

Answer 1

This solution is independent of whether the lengths of the lists in the list p are different.

library(gridExtra)  pdf("plots.pdf", onefile = TRUE) for (i in seq(length(p))) {   do.call("grid.arrange", p[[i]])   } dev.off() 

Because of onefile = TRUE the function pdf saves all graphics appearing sequentially in the same file (one page for one graphic).