D3Plus Heatmap

Following http://d3plus.org/examples/advanced/5ed41ef03b58d681cc11/

HTML

<script src="http://www.d3plus.org/js/d3.js"></script>
<script src="http://www.d3plus.org/js/d3plus.js"></script>

<div id="viz"></div>

JavaScript

var sample_data = [
  {
    "group":"MEDICINE",
    "name":"ANESTHESIOLOGY",
    "value":60.51764741,
    "risk":78.28328456,
    "url":"searchHealthcareDoctor.php?eid=7&specialty=ANESTHESIOLOGY"
  },
  {
    "group":"MEDICINE",
    "name":"INTERNAL MEDICINE",
    "value":43.05769238,
    "risk":79.44855174,
    "link":"searchHealthcareDoctor.php?eid=7&specialty=INTERNAL MEDICINE"
  },
  {
    "group":"MEDICINE",
    "name":"Emergency Medicine",
    "value":48.10188706,
    "risk":45.92837987,
    "url":"searchHealthcareDoctor.php?eid=7&specialty=Emergency Medicine"
  },
  {
    "group":"MEDICINE",
    "name":"DIAGNOSTIC RADIOLOGY",
    "value":35.19166671,
    "risk":87.17132339,
    "url":"searchHealthcareDoctor.php?eid=7&specialty=DIAGNOSTIC RADIOLOGY"
  },
  {
    "group":"MEDICINE",
    "name":"OTHER",
    "value":51.2626256,
    "risk":10.42832119,
    "url":"searchHealthcareDoctor.php?eid=7&specialty=OTHER"
  },
  {
    "group":"MEDICINE",
    "name":"OBSTETRICS/GYNECOLOGY",
    "value":61.85714278,
    "risk":60.41058053,
    "url":"searchHealthcareDoctor.php?eid=7&specialty=OBSTETRICS/GYNECOLOGY"
  },
  {
    "group":"MEDICINE",
    "name":"CARDIOVASCULAR DISEASE (CARDIOLOGY)",
    "value":59.85106388,
    "risk":93.68146283,
    "url":"searchHealthcareDoctor.php?eid=7&specialty=CARDIOVASCULAR DISEASE (CARDIOLOGY)"
  },
  {
    "group":"MEDICINE",
    "name":"Family Practice",
    "value":40.67500038,
    "risk":96.69919399,
    "url":"searchHealthcareDoctor.php?eid=7&specialty=Family Practice"
  },
  {
    "group":"MEDICINE",
    "name":"PATHOLOGY",
    "value":50.33333329,
    "risk":82.47394821,
    "url":"searchHealthcareDoctor.php?eid=7&specialty=PATHOLOGY"
  },
  {
    "group":"MEDICINE",
    "name":"HOSPITALIST",
    "value":48.2727272,
    "risk":84.16712441,
    "url":"searchHealthcareDoctor.php?eid=7&specialty=HOSPITALIST"
  },
  {
    "group":"MEDICINE",
    "name":"OBSTETRICS AND GYNECOLOGY",
    "value":2.387096733,
    "risk":23.42343101,
 ...