I would like to create such a plot using ggplot2:

(I made a small mistake here, which did not cause all the shortcuts to be displayed. Obviously, I want all the shortcuts to be displayed :)) However, my Google search query did not find anything. The closest I got was with barNest from plotrix, however I do not like the quality of the graphs that are produced. Ggplot2 look much better.
, - :
scale_x_discrete ( "Axis Title", = Level1 + Level2 + Level3)
Level1, Level2 Level3 , qplot.
, , . , scale_x_hierarchical .
:
data <- data.frame(
Subject = c(rep(1, 48), rep(2, 48), rep(3, 48), rep(4, 48)),
month = rep(c(rep(1, 12), rep(4, 12), rep(7, 12), rep(10, 12)), 4),
day = rep(c(rep(1, 4), rep(11, 4), rep(21, 4)), 16),
hour = rep(c(0, 6, 12, 18), 48),
data = rnorm(192))
, , , Spotfire.