hfill.R

library(ggplot2)


my_axis = function() {
  structure("test",
    class = c("element_custom","element_blank", "element") # inheritance test workaround
  )
}
library(grid)
# returns a gTree with desired text
element_grob.element_custom <- function(element, x,...)  {
  
  g1 <- textGrob("Low", y=0,hjust=0, rot = 90)
  g2 <- textGrob("High", y=1,hjust=1, rot = 90)
  w1 <- grobHeight(g1)
  w2 <- grobHeight(g2)
  gap <- unit(1,"npc") - w1 - w2
  g3 <- rectGrob(y = w1, vjust = 0, width = unit(1,"line"), height=gap)
  gTree(children=gList(g1, g2, g3), cl="custom_axis")
}

# gTrees don't know their size and ggplot would squash it, so give it room
grobWidth.custom_axis = heightDetails.custom_axis = function(x, ...)
  unit(1, "line")


p <- ggplot(data.frame(x=1:10), aes(x,x)) +
  geom_blank() + theme(axis.title.y  = my_axis(), plot.background = element_blank())

library(egg)

expose_layout(p)
print(p, newpage = F)