title: ggplot2 legend for plot combining geom_bar and geom_point
body: <p>I am trying to make a plot to show the returns of various securities in a portfolio in a bar plot and then superimpose points over the bars indicating exposure to those securities. However, the legend I get completely ignores the points and only draws a legend for the bars.</p>
  
  <h3>To produce a dataframe with similar structure:</h3>
  
  <pre><code>out&lt;-data.frame(security=c("A", "B", "C", "D", "A", "B", "C", "D"), avg_weight=c(0.1,0.2,0.3,0.4, 0.1, 0.2, 0.3, 0.4), return_type=c(rep("systematic",4), rep("idiosyncratic",4)), return=rnorm(8))
  </code></pre>
  
  <h3>Now, for plotting</h3>
  
  <pre><code>g &lt;- ggplot(data=out, aes(x=factor(security, levels=out$security), y=return))
  g &lt;- g + geom_bar(stat="identity", position="dodge", aes(fill=return_type))
  g &lt;- g + geom_point(aes(x=factor(security, levels=out$security), y=avg_weight))
  g &lt;- g + ggtitle("Systematic and Idiosyncratic Returns")
  g &lt;- g + theme(axis.text.x=element_text(angle=70, hjust=1))
  g + xlab("Security Description") + ylab("Return")
  </code></pre>
  
  <p><img src="https://i.stack.imgur.com/hGP8U.png" alt="Plot results"></p>
  
  <h3>How can I get a third entry in the legend, something like:</h3>
  
  <ul>
  <li>Exposure</li>
  </ul>