title: Merging two backbone collection and models into one object using underscore
body: <p>I have two backbone collections Categories and Items, Categories contains category models with id, name, and items (w/c contains item ids in string format separated by commas) and Items collection that contains item models(id, name, etc.).</p>
  
  <p>How do I merge them into one object that can be easily be rendered in a handlebars template</p>
  
  <p><strong>Sample Structure:</strong></p>
  
  <pre><code>var Categories = [{'id':'1', 'category_name':'Burgers', 'category_items':'1,2'},{'id':'2','category_name':'Drinks','category_items':'3'}];
  
  var Items = [{'id':'1','item_name':'Burger 1'},{'id':'1','item_name':'Burger 2'},{'id':'1','item_name':'Chicken; 1'}];
  </code></pre>
  
  <p><strong>Sample Output:</strong></p>
  
  <pre><code>var output = [{'id':'1', 'category_name':'Burgers', 'items':[{'id':'1','item_name':'Burger1', ...},{'id':'1','item_name':'Burger2', ...} ]}, {'id':'2', 'category_name':'Chicken', 'items':[{'id':'3','item_name':'Chicken1', ...} ]
  </code></pre>
  
  <p>And yes, i tried enough, but I can't seem to manage it</p>