How to add braces to a graph?

Question

I want to make the following graph in R:

How can I plot those horizont

Answer 1

How about something like this?

plot(c(0,1), c(0,1))
text(x = 0.5, y = 0.5, '{', srt = 90, cex = 8, family = 'Helvetica Neue UltraLight')

Adapt it to your purposes. You might find a lighter weight font or a shape you like better. There are hairline fonts if you do a search online.