D3 Examples - Nations Line Graph v2

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<!DOCTYPE html>
<head>
  <meta charset="utf-8">
  <script src="https://d3js.org/d3.v4.min.js"></script>
  <style>
    body { margin:0;position:fixed;top:0;right:0;bottom:0;left:0; }
    
    .labels {
      font-family: "Calibri";
      font-size:26px;
      stroke: gray
    }
    
    .axes{
        fill: black
    }
    
    path{
      stroke: #c7cdd6;
      stroke-width: 2;
      fill: none;
    }
    
    #lineStyle {
      fill: none;
      stroke: #5ec997;
      stroke-width: 3
    }
    
    #countrySelect{
      position:absolute;
      top:10px;
      left:100px;
        }
  </style>
</head>
​
<body>
  <script>
 
var margin = {top: 20, right: 40, bottom: 20, left: 40};
var width = 960 - margin.left - margin.right
var height = 500 - margin.top- margin.bottom
​
var svg = d3.select("body").append("svg")
    .attr("width", width + margin.left + margin.right)
    .attr("height", height + margin.top + margin.bottom)
        .append("g")
    .attr("transform", "translate(" + margin.left + "," + margin.top + ")");
​
 
  //reading the data file & setting callback function
    var data = d3.json("nations.json", main)
​
  function main(error, originalData){
        if(error) { 
            throw(error)
        };
   
//  function getCountries(input, field) {
//     var countryOptions = [];
//     for (var i=0; i < input.length ; ++i)
//         countryOptions.push({text: input[i][field], value: input[i][field]});
//     return countryOptions;
//  } 
 
    var select = d3.select('body')
    .append('select')
    .attr('class','select')
        .attr('id','countrySelect')
    .on('change', onchange)
​
  var countryOptions = originalData.map(function(a) {
        return {text: a.name, value: a.name}
    });
   
  var options = select
      .selectAll('option')
      .data(countryOptions)
      .enter()
      .append('option')
      .attr("value", function(option) { 
        return option.value; 
      })
      .text(function(option) {
        return option.text;
      })
  
    function onchange(){
  var selection = originalData.filter(function(n){
     return n.name === document.getElementById('countrySelect').value
   })[0];
​
  var line = d3.line()
        .x(function(d){ return xScale(d[0])
                    })
        .y(function(d) { return yScale(d[1])
                     });  
    
  //extents: d3.extent(data, function)
    var xExtent = d3.extent(selection.lifeExpectancy, function(d){
      return(d[0])
    });
    
    var maxLifeExpectancy = d3.max(selection.lifeExpectancy, function(d){
        return d[1]
    })
  
  //set scales
    var xScale = d3.scaleLinear()
        .domain(xExtent)
        .range([0, width]);
​
    var yScale = d3.scaleLinear()
        .domain([20, maxLifeExpectancy])
        .range([height, 0]);
 
  //set axis & call axis
    var xAxis = d3.axisBottom()
        .scale(xScale)
            .tickFormat(d3.format("d"))
​
    var yAxis = d3.axisLeft()
        .scale(yScale)
    
    svg.selectAll("*").remove();
  
    svg.append("g")
        .attr("transform", "translate (" + 0 + "," + height +")")
        .attr("class", "axes")
      .call(xAxis);
​
    svg.append("g")
      .attr("class", "axes")
      .call(yAxis);
    
    svg.append("text")
        .attr("class", "labels")
        .attr("transform", "translate(" + (width - 50) + "," + (height - 20) + ")")
        .text("Year")
​
    svg.append("text")
        .attr("class", "labels")
        .attr("transform", "rotate(-90)")
      .attr("y", margin.left)
      .attr("x",0 - (height - 300))
        .text("Life Expectancy")
      
    svg.append("path")
        .attr("id", "lineStyle")
      .datum(selection.lifeExpectancy)
      .attr("d", line);
  }
  };     
​
  </script>
</body>
​
    