title: JSON Group by count, output to key value pair json result
body: <p>I have following JSON data </p>
  
  <pre><code>"rows": [{  
          "createdDate": "3/11/2016",
          "createdBy": "Bob"          
      },{ 
          "createdDate": "3/12/2016",
          "createdBy": "Megan"            
      },{ 
          "createdDate": "3/12/2016",
          "createdBy": "Bob"          
      },{ 
          "createdDate": "3/13/2016",
          "createdBy": "Sam"          
      },{ 
          "createdDate": "3/11/2016",
          "createdBy": "Bob"          
      },]
  </code></pre>
  
  <p>And I want output for charting where I can group by any property name for count, for example here on 'createdBy' :</p>
  
  <pre><code>"result": [{
          "key": "Bob",
          "value": 3,         
      },{
          "key": "Megan",
          "value": 1,         
      },{
          "key": "Sam",
          "value": 1,         
      },
  </code></pre>
  
  <p>I have the JSON and need to manipulate it in following format before binding to my chart. I tried _groupBy from underscore but could not get desired result. </p>