title: challenge: optimize unlisting [easy]
body: <p>Because SO is a bit slow lately, I'm posting an easy question. I would appreciate it if big fishes stayed on the bench for this one and give rookies a chance to respond.</p>
  
  <p>Sometimes we have objects that have a ridiculous amount of large list elements (vectors). How would you "unlist" this object into a single vector. Show proof that your method is faster than <code>unlist()</code>.</p>