title: How to get Underscore's map to only return based on a condition
body: <p>I currently have the following:</p>
  
  <pre><code>flatArray = _.map(items, function(x){ return x.count; });
  </code></pre>
  
  <p>This returns an array like so:</p>
  
  <pre><code>[6,6,3,0,0,0,1,0]
  </code></pre>
  
  <p>How can I get just the # of items where count is Gt 0. In this case, how can I get just the number 4.</p>
  
  <p>I'm using underscore and jQuery.</p>