Normalizing y-axis in histograms in R ggplot to proportion by group

Question

My question is very similar to Normalizing y-axis in histograms in R ggplot to proportion, except that I have two groups of data of different size, and I would like that eac

Answer 1

Like this? [edited based on OP's comment]

ggplot(all,aes(x=value,fill=dataset))+
  geom_histogram(aes(y=0.5*..density..),
                 alpha=0.5,position='identity',binwidth=0.5)

Using y=..density.. scales the histograms so the area under each is 1, or sum(binwidth*y)=1. As a result, you would use y = binwidth*..density.. to have y represent the fraction of the total in each bin. In your case, binwidth=0.5.

IMO this is a little easier to interpret:

ggplot(all,aes(x=value,fill=dataset))+
  geom_histogram(aes(y=0.5*..density..),binwidth=0.5)+
  facet_wrap(~dataset,nrow=2)