How to select unique values in d3.js from data

Question

I am using the following code to populate my Combobox using d3.js

d3.csv(\"Results_New.txt\", function(data) {
dataset=data;
d3.select(\"#road\").selectAll(\"opt         


        

Answer 1

Filter your data retaining unique keys only by d3.map

d3.select("#road").selectAll("option")
    .data(d3.map(data, function(d){return d.roadname;}).keys())
    .enter()
    .append("option")
    .text(function(d){return d;})
    .attr("value",function(d){return d;});