title: How to map with underscore but without falsy values added to the result
body: <p>I have  an array of objects where I wanna only save a sub object when it pass a condition. At the moment I first use <code>map</code> and then <code>filter</code> with the result: </p>
  
  <pre><code>   var a = _.filter(
      _.map(activities.toJSON(), function (activity) {
      if (activity.verb !== 'test') {
        return activity.object;
      }
    }), function(b){return b;});
  </code></pre>
  
  <p>This seems a bit odd. Is there a better way to do this.</p>