r - Create a matrix of scatterplots (pairs() equivalent) in ggplot2

Question

Is it possible to plot a matrix of scatter plots with ggplot2, using ggplot's nice features like mapping additional factors to color, shape etc. and adding smoother?

I am thinking about something similar to the base function pairs.

Answer 1

I keep wanting to do this, but plotmatrix is crap. Hadley recommends using the GGally package instead. It has a function, ggpairs that is a vastly improved pairs plot (lets you use non-continuous variables in your data frames). It plots different plots in each square, depending on the variable types:

library(GGally)
ggpairs(iris, aes(colour = Species, alpha = 0.4))