title: Change scale from count to percentage - ggplot2 version 1.0.1
body: <p>I've tried multiple solutions to this from previous versions of ggplot answers, however, I have yet to find a way to change the scale from count to percent. </p>
  
  <p>The structure of the data includes: <code>deid</code> = an id variable; <code>variable</code> a one-level factor; and <code>value</code> = the participants response. </p>
  
  <pre><code> $ deid     : int  123 155 332 224 654 325 865 654 555 434 ...
   $ variable : Factor w/ 1 level "tx.rating": 1 1 1 1 1 1 1 1 1 1 ...
   $ value    : int  9 8 9 9 5 7 7 7 7 10 ...
  </code></pre>
  
  <p>Here is my code:</p>
  
  <pre><code>ggplot(tx.plot, aes(value, fill = variable)) + 
    geom_histogram(alpha = .6, binwidth = .5)
  </code></pre>
  
  <p>That creates:</p>
  
  <p><a href="https://i.stack.imgur.com/dYyuG.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/dYyuG.png" alt="enter image description here"></a></p>
  
  <p>I am hoping to get the percent responses from 0 - 10, not the count. I have tried to add <code>scale_y_continuous</code> and <code>scale_y_discrete</code> with the labels = percent command, however it has not worked and I receive error messages every time.</p>