D3 Examples - multiple line chart

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<!DOCTYPE html>
<head>
  <meta charset="utf-8">
  <script src="https://d3js.org/d3.v4.js"></script>
  <style>
    body { margin:0;position:fixed;top:0;right:0;bottom:0;left:0; }
    .line {
      fill: none;
      stroke: black;
      stroke-width: 1.5px;
    }
  </style>
</head>
​
<body>
  <script>
    // Margin setup
    var margin = {top: 20, right: 30, bottom: 20, left: 100},
        width = 760 - margin.left - margin.right,
        height = 300 - margin.top - margin.bottom;
        
    // Basic SVG canvas
    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 + ")");
​
    // https://bl.ocks.org/zanarmstrong/raw/05c1e95bf7aa16c4768e/
    var parseDate = d3.timeParse("%b %Y");
    var displayDate = d3.timeFormat("%b %y");
    var displayValue = d3.format(",.0f");
            
    // Temporal scale
    var x = d3.scaleTime().range([0, width]);
​
        // Linear scale
    var y = d3.scaleLinear().range([height, 0]);
    
    var line = d3.line()
    .curve(d3.curveBasis)
    .x(function(d) { return x(d.date); })
    .y(function(d) { return y(d.price); });
    
   
    var g = svg.append("g")
        .attr("transform", "translate(10, 0)");
    
    d3.text("https://gist.githubusercontent.com/mbostock/1256572/raw/44c086a6019de56dce35a47197a19468b3e4ad57/stocks.csv", function(error,raw) {
       //console.log(raw)
      // Pre-processing
      // {"id" : 1, "name": "A", "value": 10, "date": "2016-01"}
       var dsv = d3.dsvFormat(',');
       var data = dsv.parse(raw);
      //console.log(data)
      data.forEach(function(d) {
                d.date = parseDate(d.date);
        d.price = +d.price; // convertit une chaine de caractere en entier
      });
      //console.log(data)
      // pour avoir plusieurs lignes on doit avoir comme donnees un tableau de tableau
      // il trace donc le nbre de tableau dans le tableau
      
      var neasted_data = d3.nest() // fonction d3 qui fait du groupBy
          .key(function(d) { return d.symbol; })
            /*.rollup(function (leaves)//rollup permet de faire des actions sur chaque groupe
                  {return d3.sum(leaves.length,function(d) {
                    return d.price; 
                  });
                  })
          // equivaut a SELEECT SUM(Price) from table groupby symbol */
          .entries(data);
      
      console.log(neasted_data);
      
      x.domain(d3.extent(data, function(d) { return d.date; }));
            y.domain([0, d3.max(data, function(d) { return d.price; })]);
​
      g.selectAll(".line").data(neasted_data).enter()
       .append("path")
        .attr("class", "line")
        .attr("d", function(d) {return line(d.values); });
         
​
      g.selectAll(".label").data(neasted_data).enter()
       .append("text")
        .attr("class", "label")
         .text(function(d){return d.key;})
        .attr("transform", function(d,i) {
               return "translate(0," + i * 20 + ")" ;
        });
      
        svg.append("g")
        .attr("class", "axis axis--x")
        .attr("transform", "translate(0," + height + ")")
        .call(d3.axisBottom(x));
​
        svg.append("g")
        .attr("class", "axis axis--y")
        .call(d3.axisLeft(y).ticks(20));
    
    });
​
  </script>
</body>
​
    