title: Barplot with 3 categorical variable
body: <p>I have a data like this:</p>
  
  <pre><code>data &lt;- data.frame(Comp = factor(rep(2003:2004, each = 8)), 
                     Cat = rep(letters[1:4], 4), 
                     Type = rep(c('Free','Used'), each = 4), 
                     Count = trunc(rnorm(16,30,2)))
  </code></pre>
  
  <p>And I need something like a <code>barplot</code> with <code>beside = TRUE</code> and <code>beside = FALSE</code> (<code>TRUE</code> for <code>Cat</code> and <code>Comp</code>, and <code>FALSE = Type</code>).</p>
  
  <p>With this data, it will result a plot with 8 columns (Interaction of <code>Comp</code> with <code>Cat</code> (<code>Comp = 2003 + Cat = A ; Comp = 2003 + Cat = B ; ... ; Comp = 2004 + Cat = D</code>)), each one with 2 stacked columns (the levels of <code>Type</code> (<code>Free</code> and <code>Used</code>)) for <code>Count</code> variable.</p>
  
  <p>Any tip how can I do this kind of plot? I tried to do an example in EXCEL, but I failed on it too.</p>