D3 Examples - Exam Grades - Vertical Bar Chart from external JSON file

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<!DOCTYPE html>
<meta charset="utf-8">
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<head>
    <style>
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  .bar{
    fill: steelblue;
  }
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  .bar:hover{
    fill: blue;
  }
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    .axis {
      font: 10px sans-serif;
    }
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    .axis path,
    .axis line {
      fill: none;
      stroke: #000;
      shape-rendering: crispEdges;
    }
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    </style>
</head>
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<body>
    
<script src="https://d3js.org/d3.v3.min.js"></script>
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<script>
// set the dimensions of the canvas
var margin = {top: 20, right: 20, bottom: 70, left: 40},
    width = 600 - margin.left - margin.right,
    height = 300 - margin.top - margin.bottom;
​
// set the ranges
var x = d3.scale.ordinal().rangeRoundBands([0, width], .05);
​
var y = d3.scale.linear().range([height, 0]);
​
// define the axis
var xAxis = d3.svg.axis()
    .scale(x)
    .orient("bottom")
​
​
var yAxis = d3.svg.axis()
    .scale(y)
    .orient("left")
    .ticks(10);
​
​
// add the SVG element
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 + ")");
​
  
function update(myData, attr) {
​
    var fnAcc = function(d) { return d[attr]; }
  
    myData = myData.sort(function (a, b) {
    return d3.descending(a[attr], b[attr]);
  });
  
  
    wScale.domain([0, d3.max(myData, fnAcc) ]);
  
    var bars = svg.selectAll(".bars")
    .data(myData);
  
  //Enter
  var barsEnter = bars.enter()
    .append("rect")
    .attr("class", "bars")
    .attr("width", 0);
  
  //Exit
  bars.exit()
    .transition()
    .duration(1000)
    .attr("width", 0)
    .remove();
 
  //Update
  bars.merge(barsEnter)
    .attr("x", 0)
    .attr("y", function(d, i ) { return i * (BAR_HEIGHT+1);})
    .attr("height", BAR_HEIGHT)
    .style("fill", function(d,i) { return colScale(i); })
    .transition().duration(1000)
    .attr("width", function(d) { return wScale(fnAcc(d)); });
    
  xAxis
    .transition()
    .duration(1000)
    .call(d3.axisTop()
    .scale(wScale)
    .ticks(3));
}
  
// load the data
d3.json("data.json", function(error, data) {
​
    data.forEach(function(d) {
        d.code = +d.code;
        d.grade = +d.grade;
    });
  
  data.sort(function(a, b) {
    return a.grade - b.grade;
  });
    
  // scale the range of the data
  x.domain(data.map(function(d) { return d.code; }));
  y.domain([0, d3.max(data, function(d) { 
    return d.grade; })]);
​
  // add axis
  svg.append("g")
      .attr("class", "x axis")
      .attr("transform", "translate(0," + height + ")")
      .call(xAxis)
    .selectAll("text")
      .style("text-anchor", "end")
      .attr("dx", "-.8em")
      .attr("dy", "-.55em")
      .attr("transform", "rotate(-90)" );
​
  svg.append("g")
      .attr("class", "y axis")
      .call(yAxis)
    .append("text")
      .attr("transform", "rotate(0)")
      .attr("y", -10)
      .attr("dy", ".71em")
      .style("text-anchor", "middle")
      .text("Grade Scale");
  
  
  // Add bar chart
  svg.selectAll("bar")
      .data(data)
    .enter().append("rect")
      .attr("class", "bar")
      .attr("x", function(d) { return x(d.code); })
      .attr("width", x.rangeBand())
      .attr("y", function(d) { return y(d.grade); })
      .attr("height", function(d) { return height - y(d.grade); }).sort();
​
  console.log(data);
  //update(data);
  
});
​
</script>
​
</body>
​
    