title: how to add multiple boxplots to same axis set
body: <p>I'm trying to plot 4 groups of data as boxplots on the same set of axis.
  I've been able to use the <code>print()</code> function to plot them on separate plots, but can't figure out how to plot them all together, preferably using the base package or lattice</p>
  
  <p>below is some code I am trying, but it keeps coming up with error:</p>
  
  <pre><code>Error in x[floor(d)] + x[ceiling(d)] :
  non-numeric argument to binary operator
  </code></pre>
  
  <p>Heres the code I'm currently trying:</p>
  
  <pre><code>Summer &lt;- SeasonalMax$Summer
  Autumn &lt;- SeasonalMax$Autumn
  Winter &lt;- SeasonalMax$Winter
  Spring &lt;- SeasonalMax$Spring
  
  boxplot(Summer, Autumn, Winter, Spring,
      main = "Multiple boxplots for comparision",
      at = c(1,2,3,4),
      names = c("Summer", "Autumn", "Winter", "Spring"),
      las = 2,
      col = c("red","orange", "blue", "pink"))
  </code></pre>