r - Multiple ggplots of different sizes

Question

It's relatively simple using grid.arrange in the gridExtra package to arrange multiple plots in a matrix, but how can you arrange plots (the ones I'm working on are from ggplot2) when some plots are intended to be larger than others? In base, I can use layout() such as in the example below:

 nf <- layout(matrix(c(1,1,1,2,3,1,1,1,4,5,6,7,8,9,9), byrow=TRUE, nrow=3))
 layout.show(nf)

what is the equivalent for ggplot plots?

Some plots for inclusion

library(ggplot2)
p1 <- qplot(x=wt,y=mpg,geom="point",main="Scatterplot of wt vs. mpg", data=mtcars)
p2 <- qplot(x=wt,y=disp,geom="point",main="Scatterplot of wt vs disp", data=mtcars)
p3 <- qplot(wt,data=mtcars)
p4 <- qplot(wt,mpg,data=mtcars,geom="boxplot")
p5 <- qplot(wt,data=mtcars)
p6 <- qplot(mpg,data=mtcars)
p7 <- qplot(disp,data=mtcars)
p8 <- qplot(disp, y=..density.., geom="density", data=mtcars)
p9 <- qplot(mpg, y=..density.., geom="density", data=mtcars)

Answer 1

You can use nested arrangeGrob calls like this example:

library(ggplot2)
library(gridExtra)

p <- ggplot(data.frame(x=1, y=1), aes(x,y)) + geom_point()

grid.arrange(
  arrangeGrob(
    p, 
    arrangeGrob(p, p, nrow=2),
    ncol=2 ,widths=c(2,1)),
  arrangeGrob(p, p ,p ,ncol=3, widths=rep(1,3)),
  nrow=2)

Edit:

gl <- lapply(1:9, function(ii) grobTree(rectGrob(),textGrob(ii)))

grid.arrange(
  arrangeGrob(gl[[1]],
              do.call(arrangeGrob, c(gl[2:5], ncol=2)),
              nrow=1,
              widths=3:2),
  do.call(arrangeGrob, c(gl[6:9], nrow=1, list(widths=c(1,1,1,2)))),
nrow=2, heights=c(2,1))