title: how to get unique array based of nested attribute using underscore.js
body: <p>I have a json array like this :</p>
  
  <pre><code>myArray=[{ a:1,
            b:[{c:"x",d:"y"}, {c:"r", d:"s"}...]
           },
           { a:2,
            b:[c:"p",d:"q"}, {c:"x", d:"s"}...]
           }
           ...
          ]
  </code></pre>
  
  <p>Is it possible to get a subset of myArray with unique values of "c" using underscore.js?</p>