Filter/group google maps markers

google_maps_markers.js

    {# Map #}
    <script type="text/javascript">
      var map = new google.maps.Map(document.getElementById("map"), {
        zoom: 6,
        center: new google.maps.LatLng(-32.574592,-55.20605),
        mapTypeControl: true,
        mapTypeControlOptions: {style: google.maps.MapTypeControlStyle.DROPDOWN_MENU},
        scrollwheel: false,
        streetViewControl: false,
        mapTypeId: google.maps.MapTypeId.TERRAIN
      });

      {# Markers #}
      var markers = {};
      {% for project in project_list %}

        {% if project.latitude and project.longitude %}
          var marker = new google.maps.Marker({
              position: new google.maps.LatLng({{ project.latitude }}, {{ project.longitude }}),
              map: map,
              title: "{{ project.title }}"
          });
          {# Marker filter #}
          category = '{{ project.category.slug }}'
          if (typeof markers[category] == "undefined") {
            markers[category] = [marker]
          } else {
            markers[category].push(marker)
          }
          {# Marker info window #}
          {% url project_detail project.slug as url %}
          var infowindow = new google.maps.InfoWindow({
            content: '<h2><a href="{{ url }}">{{ project.title }}</a></h2><p>{{ project.short_description }}</p><p>{{ project.location }}</p><p><a href="{{ url }}">{% trans "View details" %} &raquo;</a></p>',
          });
          google.maps.event.addListener(marker, 'click', function() {
            infowindow.open(map, marker);
          });
        {% endif %}
      {% endfor %}
    </script>