title: using _.reject turns my object into an array
body: <p>I have some data that I want to iterate through and reject those with a <code>disabled: true</code> property.</p>
  
  <p>however when I try <code>_.reject</code> my object gets turned into an array.</p>
  
  <pre><code>var data = {
    stuff: {
       item1: {
          name: "one",
          disabled: true
       },
       item2: {
          name: "two"
       }
  
    }
  };
  
  
  data.stuff = _.reject(data.stuff, function(val){
      return val.disabled;
  });
  </code></pre>
  
  <p><code>data.stuff</code> is now an array, rather than an Object. I've lost all my keys.</p>