title: Calculations with comprehensions
body: <p>Let's say I have the following:</p>
  
  <pre><code>scoringObject = 
    a : -1
    b : 0
    c : 1
    d : 2
  
  resultsArray = ['a','c','b','b','c','c','d']
  </code></pre>
  
  <p>Using Coffescript, how can I calculate aggregateScore (+4 in the example) ?</p>