Add curly braces to ggplot2 and then use ggsave

Question

So this is very relevant to this question and this answer is an excellent solution.

The problem is that when I try to export the plot using ggsave the curly braces aren\

Answer 1

I don't understand the logic used in grid.brackets but it would help if there was a bracketsGrob function that would simply return a grob without drawing it. Perhaps contact the maintainer with a feature request?

Anyway, assuming such a function was available, it can be fed to annotation_custom making it compatible with ggsave.

bracketsGrob <- function(...){
l <- list(...)
e <- new.env()
e$l <- l
  grid:::recordGrob(  {
    do.call(grid.brackets, l)
  }, e)
}

# note that units here are "npc", the only unit (besides physical units) that makes sense
# when annotating the plot panel in ggplot2 (since we have no access to 
# native units)

b1 <- bracketsGrob(0.33, 0.05, 0, 0.05, h=0.05, lwd=2, col="red")
b2 <- bracketsGrob(1, 0.05, 0.66, 0.05, h=0.05,  lwd=2, col="red")

p <- the_plot + 
  annotation_custom(b1)+ 
  annotation_custom(b2) +
  scale_y_continuous(expand=c(0.11,0))
p

ggsave("test.png", p, width = 4, height = 2.5)