How to draw a box/border around plots arranged side by side using grid.arrange in R

Question

I have created two plots using ggplot as follows:

library(ggplot2)
library(gridExtra)
g1 <- ggplot(iris, aes(Sepal.Width, Sepal.Length)) + geom_point()
g2 <- ggplot(iris, aes(Petal.Width, Petal.Length)) + geom_point()
grid.arrange(g1, g2, ncol=2)

I would like to draw a border/box around the two side by side plots produced by grid.arrange...I think it is something to do with using grid.border, but am not sure of how exactly to do so. Will appreciate any help?

Answer 1

Using an example from the ggplot help page:

 gg <- df <- data.frame(gp = factor(rep(letters[1:3], each = 10)),
                  y = rnorm(30))

 library(plyr)
 ds <- ddply(df, .(gp), summarise, mean = mean(y), sd = sd(y))
 gg2 <-ggplot(df, aes(x = gp, y = y)) +
    geom_point() +
    geom_point(data = ds, aes(y = mean),
               colour = 'red', size = 3)+theme(panel.border=element_rect(fill=NA) )
 grid.arrange(gg2,gg2, ncol=2)

Or perhaps this depending on your meeaning:

 gg2 <-ggplot(df, aes(x = gp, y = y)) +
    geom_point() +
    geom_point(data = ds, aes(y = mean),
               colour = 'red', size = 3)+theme(plot.background = element_rect(size=3,linetype="solid",color="black"))
 grid.arrange(gg2,gg2, ncol=2)

If you just want a bordering rectangle:

grid.rect(.5,.5,width=unit(.99,"npc"), height=unit(0.99,"npc"), 
          gp=gpar(lwd=3, fill=NA, col="blue"))