percentage on y lab in a faceted ggplot barchart?

Question

doing facets in ggplot I would often like the percentage to be used instead of counts.

e.g.

test1 <- sample(letters[1:2], 100, replace=T)
test2 &         


        

Answer 1

A very simple way:

ggplot(test, aes(test2)) + 
    geom_bar(aes(y = (..count..)/sum(..count..))) + 
    facet_grid(~test1)

So I only changed the parameter of geom_bar to aes(y = (..count..)/sum(..count..)). After setting ylab to NULL and specifying the formatter, you could get:

ggplot(test, aes(test2)) +
    geom_bar(aes(y = (..count..)/sum(..count..))) + 
    facet_grid(~test1) +
    scale_y_continuous('', formatter="percent")

Update Note that while formatter = "percent") works for ggplot2 version 0.8.9, in 0.9.0 you'd want something like scale_y_continuous(labels = percent_format()).