Variable Width Bar Plot

Question

I\'d like to produce an area/bar graph in R similar to this:

Answer 1

Inspired by the code from the blog post I mentioned above,

df <- data.frame(x = c("Alpha", "Beta", "Gamma", "Delta"), width = c(25, 50, 75, 100), height = c(100, 75, 50, 25))
df$w <- cumsum(df$width)
df$wm <- df$w - df$width
df$wt <- with(df, wm + (w - wm)/2)

library(ggplot2)
p  <- ggplot(df, aes(ymin = 0))
p1 <- p + geom_rect(aes(xmin = wm, xmax = w, ymax = height, fill = x))
library(grid) # needed for arrow function
p1 + geom_text(aes(x = wt, y = height * 0.8, label = x)) + 
     theme_bw() + labs(x = NULL, y = NULL) + 
     theme(axis.ticks = element_blank(),axis.text.x = element_blank(), 
     axis.text.y = element_blank(), legend.position = "none") + 
     annotate("text", x = 120, y = 83, label = "a Beta block") + 
     geom_segment(aes(x = 100, y = 80, xend = 80, yend = 75), 
     arrow = arrow(length = unit(0.5, "cm")))