title: How can I plot to multiple devices at the same time?
body: <p>When I am plotting, I often plot to an <code>eps</code> file and a <code>png</code> file like this:</p>
  
  <pre><code>postscript(file=paste(dir, output, "_ggplot.eps", sep=""), onefile=FALSE, horizontal=FALSE, width=4.8, height=4.0)
  # Plotting code
  dev.off()
  
  png(paste(dir, output, "_ggplot.png", sep=""), width=450, height=300)
  # Plotting code
  dev.off()
  </code></pre>
  
  <p>The problem is that the plotting code is repeated twice. Is it possible to specify multiple devices for plotting?</p>