Annotate the axis ggplo2

Question

I am trying to create an annotation (particularly a rectangle) over a ggplot. Here's what I want to get:

I have tried geom_rect but that can only draw inside the plot axis. I have also attempted to use annotate_custom which this post mentions, but when I try to work with xmin = -3 (for instance), it doesn't work.

Thank you!

Answer 1

I'm gonna start by asking what you are trying to achieve with this? It seems odd, at least in your example.

But, it can be done. Because you did not provide a reproducible example, I've got something else. The goal here is to turn of the panel's clipping, such that elements that lie outside it's boundaries will be plotted.

library(ggplot2)
library(grid)

# Create a plot
p <- ggplot(mtcars, aes(wt, mpg)) + geom_point()

Here, I'm adding a rectangle with rect. But this also modifies the x- and y-axis, so we fix these with coord_cartesian. You cannot use xlim as this will remove data points that fall outside the range.

g <- p +  annotate('rect', xmin=-1, xmax=3, ymin=10, ymax=30, fill='blue', alpha=1/3) +
  coord_cartesian(xlim=c(1, 4))

# Convert into a graphical object -- a grob
g <- ggplotGrob(g)

# Try printing g

g is an object that puts all the elements into a table-like structure. So now, we find the panel in the layout dataframe of g, and turn of clipping.

i <- which(g$layout$name == 'panel')
g$layout[i,'clip'] <- 'off'

Finally draw the grob:

# grid.newpage()
grid.draw(g)