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

Here is a within ggplot method, using ..count.. and ..PANEL..:

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

As this is computed on the fly, it should be robust to changes to plot parameters.