Add a footnote citation outside of plot area in R?

Question

I\'d like to add a footnote citation to my 3-panel facet grid plot produced in R. It\'s a footnote to credit the data source. I\'d ideally like to have it below and external t

Answer 1

library(gridExtra)
library(grid)
library(ggplot2)

g <- grid.arrange(qplot(1:10, 1:10, colour=1:10) + labs(caption="ggplot2 caption"), 
              bottom = textGrob("grid caption", x = 1, 
                                hjust = 1, gp = gpar(fontface = 3L, fontsize = 9)))
ggsave("plot.pdf", g)

Edit: note that this solution is somewhat complementary to the recent caption argument added to ggplot2, since the textGrob can here be aligned with respect to the whole figure, not just the plot panel.