title: Iterate through records and storing into an array
body: <p>I need to display a table likes this:</p>
  
  <p><a href="http://i.stack.imgur.com/5XSKc.png" rel="nofollow">Table</a></p>
  
  <p>I need the total of Products of each month grouped by Tier. But I need to display 0 if nothing is found. I'm using</p>
  
  <p>Product belongs_to :tier
  Tier has_many :products</p>