title: Plotting two variables using ggplot2 - same x axis
body: <p>I have two graphs with the same x axis - the range of x is 0-5 in both of them.
  I would like to combine both of them to one graph and I didn't find a previous example.
  Here is what I got:</p>
  
  <pre><code>c &lt;- ggplot(survey, aes(often_post,often_privacy)) + stat_smooth(method="loess")
  c &lt;- ggplot(survey, aes(frequent_read,often_privacy)) + stat_smooth(method="loess")
  </code></pre>
  
  <p>How can I combine them?
  The y axis is "often privacy" and in each graph the x axis is "often post" or "frequent read". 
  I thought I can combine them easily (somehow) because the range is 0-5 in both of them. </p>
  
  <p>Many thanks!</p>