title: Selecting random tuple from bag
body: <p>Is it possible to (efficiently) select a random tuple from a bag in pig? 
  I can just take the first result of a bag (as it is unordered), but in my case I need a proper random selection.
  One (not efficient) solution is counting the number of tuples in the bag, take a random number within that range, loop through the bag, and stop whenever the number of iterations matches my random number. Does anyone know of faster/better ways to do this?</p>