p <- ggplot(mtcars, aes(wt, mpg))
p + geom_point()
p + geom_point() + geom_rug()
p + geom_point() + geom_rug(sides="b") # Rug on bottom only
p + geom_point() + geom_rug(sides="trbl") # All four sides
p + geom_point() + geom_rug(position='jitter')
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