Create hex bins on the fly

<!DOCTYPE html>
<html>
  <head>
    <title>Client side hexgrid | CartoDB.js</title>
    <meta name="viewport" content="initial-scale=1.0, user-scalable=no" />
    <meta http-equiv="content-type" content="text/html; charset=UTF-8"/>
    <link rel="shortcut icon" href="https://cartodb.com/assets/favicon.ico" />
    <style>
      html, body, #map {
        height: 100%;
        padding: 0;
        margin: 0;
      }
    </style>

</head>
  <body>
    <div id="map"></div>

<script src="https://libs.cartocdn.com/cartodb.js/v3/cartodb.js"></script>
    <script>
      // use your initial zoom size to set a base grid size
      // it doesn't need to change on zoom or anything...
      var zoom = 5; // init zoom
      function createBinStyle(tablename, multiplier, ramp){
        // setup SQL client
        var sql = cartodb.SQL({ user: 'andrew' });
        // get the extents of a new grid
        sql.execute("WITH hgrid AS (SELECT CDB_HexagonGrid(ST_Expand(!bbox!, greatest(CDB_XYZ_Resolution("+zoom+")) * "+multiplier+"), CDB_XYZ_Resolution("+zoom+") * "+multiplier+") as cell), aggs AS (SELECT count(i.cartodb_id)/power( "+multiplier+" * CDB_XYZ_Resolution("+zoom+"), 2 ) as points_density FROM hgrid, (select * from "+tablename+") i where ST_Intersects(i.the_geom_webmercator, hgrid.cell) GROUP BY hgrid.cell) SELECT min(points_density) mn, max(points_density) mx FROM aggs")
          .done(function(data){
            // calculate the new steps for CartoCSS
            var step = (data.rows[0].mx - data.rows[0].mn) / ramp.length;
            if (step==0) step = 1;
            var newstyle = "#"+tablename+"{polygon-opacity: 0.8; line-color: #FFF; line-width: 1; line-opacity: 1; ";
            for(var i = data.rows[0].mx; i>data.rows[0].mn; i=i-step){
              var fill = ramp.pop();
              newstyle += "[points_density <= "+i+"] {polygon-fill: "+fill+";} ";
            }
            newstyle+= "}";
            // Set new style
            sublayer.setCartoCSS(newstyle)
          })

}
      function main() {

// create leaflet map
        var map = L.map('map', { 
          zoomControl: false,
          center: [-30, 27],
          zoom: zoom
        })

// add a base layer
        L.tileLayer('https://tile.stamen.com/toner/{z}/{x}/{y}.png', {
          attribution: 'Stamen'
        }).addTo(map);

// add cartodb layer with one sublayer
        var sublayer;

// !pxel_width! and !pixel_height! are provided by the tiler
        cartodb.createLayer(map, {
          user_name: 'andrew',
          type: 'cartodb',
          sublayers: [{
             sql: 'WITH hgrid AS (SELECT CDB_HexagonGrid(ST_Expand(!bbox!, greatest(!pixel_width!,!pixel_height!) * 15), greatest(!pixel_width!,!pixel_height!) * 15) as cell) SELECT hgrid.cell as the_geom_webmercator, count(i.cartodb_id) as points_count, count(i.cartodb_id)/power( 15 * CDB_XYZ_Resolution('+zoom+'), 2 ) as points_density, 1 as cartodb_id FROM hgrid, (select * from za) i where ST_Intersects(i.the_geom_webmercator, hgrid.cell) GROUP BY hgrid.cell',
             cartocss: '#za{ polygon-fill: #BD0026; polygon-opacity: 0.8; line-color: #FFF; line-width: 1; line-opacity: 1; } #za{ [points_density <= 2.03359309142757e-7] { polygon-fill: #BD0026; } [points_density <= 7.54008032072687e-8] { polygon-fill: #F03B20; } [points_density <= 5.49720141609644e-8] { polygon-fill: #FD8D3C; } [points_density <= 3.95575642442075e-8] { polygon-fill: #FECC5C; } [points_density <= 2.21002354228201e-8] { polygon-fill: #FFFFB2; } }',
             interactivity: 'cartodb_id, points_count',
             infowindow: false
          }]
        })
        .addTo(map)
        .done(function(layer) {

sublayer = layer.getSubLayer(0);
          sublayer.setInteraction(true);

var infobox = new cdb.geo.ui.InfoBox({
            width: 300,
            layer: layer,
            template: '<p>points: {{points_count}}</p>'
          });

$("body").append(infobox.render().el);

setTimeout(function(){
	        // table we are visualizing
	        var tablename = "za";
	        // the smaller the smaller the grid
	        var multiplier = 5; //note: originally it was 15
	        // our color ramp
	        var ramp = ['#BD0026','#F03B20','#FD8D3C','#FECC5C','#FFFFB2'];

// custom function
	        createBinStyle(tablename, multiplier, ramp)

// Set new SQL (see "* 5" instead of "* 15" in original)
            sublayer.setSQL("WITH hgrid AS (SELECT CDB_HexagonGrid(ST_Expand(!bbox!, greatest(!pixel_width!,!pixel_height!) * "+multiplier+"), greatest(!pixel_width!,!pixel_height!) * "+multiplier+") as cell) SELECT hgrid.cell as the_geom_webmercator, count(i.cartodb_id) as points_count, count(i.cartodb_id)/power( "+multiplier+" * CDB_XYZ_Resolution("+zoom+"), 2 ) as points_density, 1 as cartodb_id FROM hgrid, (select * from za) i where ST_Intersects(i.the_geom_webmercator, hgrid.cell) GROUP BY hgrid.cell");
          },2000)
        });

}

// you could use $(window).load(main);
      window.onload = main;

</script>

</body>
</html>

Modified http://libs.cartocdn.com/cartodb.js/v3/cartodb.js to a secure url

https://libs.cartocdn.com/cartodb.js/v3/cartodb.js