title: Using guide_legend with geom_bar in ggplot
body: <p>Is there anyway of making geom_legend work with geom_bar? I want to have too lines in my legend. It works for geom_line but not for geom_bar charts.</p>
  
  <p>It works fine when I used it here:</p>
  
  <pre><code>ggplot(diamonds, aes(x,y)) + 
        geom_point(aes(colour = z))+
        guides(col = guide_legend(ncol = 2))
  </code></pre>
  
  <p>The code it doesn't work for is as follows: </p>
  
  <pre><code>ggplot(diamonds, aes(clarity, fill=cut)) + 
         geom_bar()+
         guides(col = guide_legend(ncol = 2))
  </code></pre>
  
  <p>Thanks for your help.</p>