title: How to select unique values in d3.js from data
body: <p>I am using the following code to populate my Combobox using d3.js</p>
  
  <pre><code>d3.csv("Results_New.txt", function(data) {
  dataset=data;
  d3.select("#road").selectAll("option")
  .data(data).enter().append("option").text(function(d){return d.roadname;}).attr("value",function(d){return d.roadname;});
  });
  </code></pre>
  
  <p>There are different rows with the same name. The combobox is populating with these duplicate names. For example in multiple rows the name of the road is I-80.But in the combobox I want to see I-80 only once. How can I do that?</p>