title: ggplot: relative frequencies of two groups
body: <p>I want a plot like this except that each facet sums to 100%.  Right now group M is 0.05+0.25=0.30 instead of 0.20+0.80=1.00.</p>
  
  <pre><code>df &lt;- rbind(
      data.frame(gender=c(rep('M',5)), outcome=c(rep('1',4),'0')),
      data.frame(gender=c(rep('F',10)), outcome=c(rep('1',7),rep('0',3)))
  )
  
  df
  
  ggplot(df, aes(outcome)) +
      geom_bar(aes(y = (..count..)/sum(..count..))) +
      facet_wrap(~gender, nrow=2, ncol=1) 
  </code></pre>
  
  <p>(Using y = ..density.. gives worse results.)</p>