title: Lodash reject get return object
body: <pre><code>var obj = {a: [], b: [1,2], c: [], d: [1]};
  </code></pre>
  
  <p>How do I get a non-empty array of objects like the following:</p>
  
  <pre><code>{b: [1,2], d: [1]}
  </code></pre>