D3 Examples - D3 aggregation tutorial

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<!DOCTYPE html>
<head>
  <style>
​
.axis .domain {
  display: none;
}
</style>
</head>
<body>
<svg width="960" height="500"></svg>
<script src="https://d3js.org/d3.v4.min.js"></script>
<script>
        // Chart initialization
    var svg = d3.select("svg"),
    margin = {top: 20, right: 20, bottom: 30, left: 40},
    width = +svg.attr("width") - margin.left - margin.right,
    height = +svg.attr("height") - margin.top - margin.bottom,
    g = svg.append("g").attr("transform", "translate(" + margin.left + "," +    margin.top + ")");
        
    // X axis
    var x = d3.scaleBand()
      .rangeRound([0, width])
      .paddingInner(0.1);
        
    // y axis
    var y = d3.scaleLinear()
      .rangeRound([height, 0]);
        
    //load data
    d3.csv("data_task_10.csv", function(data){
        //console.log(data);
      
      // Group by priority
      var nested_data = d3.nest()
                .key(function(d) { return d.priority; })        
            .rollup(function(leaves) {return {"length": leaves.length, "total_time": d3.sum(leaves, function(d) {return parseFloat(d.time);})} })
                .entries(data)
      
      console.log(nested_data); 
      
      // Color scale
      var z = d3.scaleOrdinal(d3.schemeCategory10);
      
      // Set domains of axes scales
      x.domain(nested_data.map(function(d) { return d.key; }));
      y.domain([0, d3.max(nested_data, function(d) { return d.value.total_time; })]);
      z.domain(nested_data.map(function(d) { return d.key; }))
            
      // Draw rect
      g.selectAll("rect")
        .data(nested_data)
        .enter().append("rect")
      .attr("x", function(d) { return x(d.key); })
      .attr("y", function(d) { return y(d.value.total_time); })
      .attr("height", function(d) { return height - y(d.value.total_time);})
      .attr("width", x.bandwidth())
      //.attr("fill", "red") 
      .attr("fill", function(d,i) { return z(d.key); })
        
      // Draw x axis
      g.append("g")
      .attr("class", "axis")
      .attr("transform", "translate(0," + height + ")")
      .call(d3.axisBottom(x));
            
      // Draw y axis
        g.append("g")
        .attr("class", "axis")
        .call(d3.axisLeft(y).ticks(null, "s"))
    
      
      
    });
​
  </script>
</body>
​
    