title: Google map API : apply MarkerClusterer only to a category of specific markers
body: <p>Using MarkerClusterer, I would like to cluster only a category of markers.
  I have here 10 markers. I want to cluster only 8 of them, using a "type" variable, that is either "cluster", or "nocluster".</p>
  
  <p>Sounds simple, but I didn't find any tip to do that...
  Any idea?</p>
  
  <p>Thank you</p>
  
  <pre><code>&lt;script&gt;
  
      function initMap() {
  
        var map = new google.maps.Map(document.getElementById('map'), {
          zoom: 8,
          center: {
            lat: 48.371310,
            lng: 7.593634
          },
          gestureHandling: 'cooperative'
        });
  
        var markers1 = locations.map(function(location, i) {
  
          var marker = new google.maps.Marker({
            position: location,
            type: location.type
          });
  
        });
  
        // Add a marker clusterer to manage the markers. 
        var mcOptions = {gridSize: 50, maxZoom: 10, styles: [{
          anchor:[0,0],
          textSize: 14,
          height: 50,
          width: 50
        }]
      };
  
        var markerCluster = new MarkerClusterer(map, markers1, mcOptions);
  
      } /* end FUNCTION initMap */
  
      var locations = [
              {num: '1', type: 'cluster', lat: 49.050288, lng: 7.950412},
              {num: '2', type: 'cluster', lat: 48.929413, lng: 7.852254},
              {num: '3', type: 'cluster', lat: 48.926529, lng: 7.361955},
              {num: '4', type: 'cluster', lat: 48.892072, lng: 7.655839},
              {num: '5', type: 'cluster', lat: 48.887685, lng: 7.785195},
              {num: '6', type: 'cluster', lat: 48.857382, lng: 7.321078},
              {num: '7', type: 'cluster', lat: 48.856634, lng: 7.319182},
              {num: '8', type: 'cluster', lat: 48.761871, lng: 7.967141},
              {num: '9', type: 'nocluster', lat: 48.736924, lng: 7.709988},
              {num: '10', type: 'nocluster', lat: 48.749944, lng: 7.340100}
            ];
  
      google.maps.event.addDomListener(window, "load", initMap);
  
  &lt;/script&gt;
  
  &lt;script src="js/markerclusterer.js"&gt;&lt;/script&gt;
  </code></pre>