title: Sum objects with similar key values
body: <p>I have an array of objects like so:</p>
  
  <pre><code>var objects = [{a:'b',c:'d',count:1},{a:'b',c:'d',count:2},{a:'y',c:'d',count:4}]
  </code></pre>
  
  <p>I want to sum all the counts that have the same <code>a</code> and <code>b</code> values to make something like so: </p>
  
  <pre><code>{a:'b',c:'d',count:3},{a:'y',c:'d',count:4}
  </code></pre>
  
  <p>Is there an easy way to do this?</p>