title: What is the object equivalent of _.pluck
body: <p>I've re-implemented my own version of what I need but I suspect this is already included in underscore since it's so simple and so closely related to many other functions. But I can't think of what it should be called.</p>
  
  <p>Basically, what I want is a version of _.pluck that works with objects and returns an object instead of an array (with its associated keys).</p>
  
  <p>So, for instance, if I had an object like this:</p>
  
  <pre><code>elements: {
      steam: {
          temperature: 100,
          color: 'orange',
          state: 'gas'
      },
      water: {
          temperature: 50,
          color: 'blue',
          state: 'liquid'
      },
      ice: {
          temperature: 0,
          color: 'white',
          state: 'solid'
      }
  }
  </code></pre>
  
  <p>I'd want to call <code>_.something(elements, 'temperature')</code></p>
  
  <p>And have it return</p>
  
  <pre><code>{
      steam: 100,
      water: 50,
      ice: 0
  }
  </code></pre>
  
  <p>Instead of <code>_.pluck(elements, 'temperature')</code> which returns</p>
  
  <pre><code>[100, 50, 0]
  </code></pre>
  
  <p>What is this transformation called and is it already included in underscore? I've written a quick version myself with jQuery's each loop since I'm more familiar with jQuery than underscore (included below) but would prefer to use one from the library if possible.</p>
  
  <pre><code>$.objPluck = function(obj, key) {
      var ret = {};
      $.each(obj, function(k, value) {
          ret[k] = value[key];
      });
      return ret;
  }
  </code></pre>