title: Plotting several groups of box plots side-by-side in R
body: <p>I am trying to plot two box-plots in the same plot, each within the same category. 
  I can generate the boxplots individually, but am stumped when I try to get them onto the same graph.</p>
  
  <p>Here is what I have so far:</p>
  
  <pre><code>a&lt;-matrix(nrow=100,ncol=3,data=runif(300,max=2))
  b&lt;-matrix(nrow=100,ncol=3,data=runif(300,max=1))
  colnames(a)&lt;-c("case 1","case 2","case 3")
  colnames(b)&lt;-c("case 1","case 2","case 3")
  boxplot(cbind(a,b))
  </code></pre>
  
  <p>This plot results in 6 boxplots, first 3 for a, then 3 for b.</p>
  
  <p>Is there a trick/simple option that I am missing that will give me
  first value for a and b, then second and finally the third set of values, all plotted in such a way there are is only three ticks on the x-axis, one for each of the sets?</p>
  
  <p>Any pointers greatly appreciated,</p>
  
  <p>Iain</p>