title: Create barplot from data.frame
body: <p>In R I have a data.frame like the one on the top of the picture.</p>
  
  <p>Is there a possibility to create a barplot like below?</p>
  
  <p>data.frame:</p>
  
  <pre><code>      X1   X2   X3  
   --- ---- ---- ---- 
    A    2   3    4   
    B    4   2    1   
    C    1   NA   NA  
  </code></pre>
  
  <p>Barplot:</p>
  
  <pre><code>----------------------------
  |                          |
  |       #    #             |
  |    #  #    #             |
  | #  #  #    #  #          |
  | #  #  #    #  #  #    #  |
  ----------------------------
    X1 X2 X3   X1 X2 X3   x1
       A           B       C
  </code></pre>