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 <- sample(letters[3:8], 100, replace=T) test <- data.frame(cbind(test1,test2)) ggplot(test, aes(test2))+geom_bar()+facet_grid(~test1) 

This is very easy but if N is different in facet A compared to facet B, it would be better I think, to compare percentages, in such a way that the each facet sums to 100%.

how would you achieve this?

Hope my question makes sense.

Sincerely.

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.

Answer 2

Try this:

# first make a dataframe with frequencies df <- as.data.frame(with(test, table(test1,test2))) # or with count() from plyr package as Hadley suggested df <- count(test, vars=c('test1', 'test2')) # next: compute percentages per group df <- ddply(df, .(test1), transform, p = Freq/sum(Freq)) # and plot ggplot(df, aes(test2, p))+geom_bar()+facet_grid(~test1) 

You could also add + scale_y_continuous(formatter = "percent") to the plot for ggplot2 version 0.8.9, or + scale_y_continuous(labels = percent_format()) for version 0.9.0.