title: how to transform jArray into jobject
body: <p>I'm using <code>Newtonsoft.Json</code> lib with C# and encountered a problem. I have a jArray as below:</p>
  
  <pre><code>[{"category": "computer","subcat": "desktop"},
   {"category": "category","subcat": "laptop"},
   {"category": "television","subcat": "LCD"}]
  </code></pre>
  
  <p>and I want it to be transformed as a jObject as below: </p>
  
  <pre><code>{"computer": ["desktop","laptop"],
   "television": ["LCD"]}
  </code></pre>
  
  <p>Here want I need is a general method that can handle this type of transformation. Which means this method could also do the trick even if the jArray has a 3rd level property. e.g.</p>
  
  <p><strong>from</strong> </p>
  
  <pre><code>[{"typeA":"a","typeB":"a1","typeC":"a11"},{"typeA":"a","typeB":"a1","typeC":"a12"},
   {"typeA":"a","typeB":"a2","typeC":"a21"}]
  </code></pre>
  
  <p><strong>to</strong></p>
  
  <pre><code>{"a":{"a1":["a11","a12"],"a2":["a21"]}}
  </code></pre>
  
  <p>Thanks a lot!</p>