title: Boxplot with Subgroups in R
body: <p>I am trying to make a <a href="http://i.stack.imgur.com/oDafV.jpg" rel="nofollow">Boxplot with subgroups</a> in R.</p>
  
  <p>My data looks like this:</p>
  
  <pre><code>Sample Point    N.conc  toc
  H1  0.2 0.2
  H1  0.3 0.3
  H1  0.4 0.4
  H1  0.3 0.3
  H1  0.3 0.3
  H1  0.5 0.5
  H1  0.5 0.5
  H1  0.4 0.4
  H1  0.1 0.1
  H2  0.4 0.4
  H2  0.5 0.5
  H2  0.5 0.6
  H2  0.4 0.5
  H2  0.1 0.1
  H2  0.3 0.3
  H2  0.4 0.4
  H2  0.3 0.3
  H2  0.3 0.3
  H3  0.4 0.4
  H3  0.5 0.8
  H3  0.3 0.3
  H3  0.2 0.2
  H3  0.2 0.2
  H3  0.4 0.4
  H3  0.3 0.3
  H3  0.2 0.2
  H3  0.3 0.4
  </code></pre>
  
  <p>How can I make a boxplot similar to the <a href="http://i.stack.imgur.com/oDafV.jpg" rel="nofollow">attached picture</a>?</p>