D3 Examples - Exam Grades - Vertical Bar Chart

Exam Grades - Vertical Bar Chart

This simple bar chart is constructed from a TSV file storing the exam grades of students in an imaginary Visual Analytics class. The chart employs conventional margins and a number of D3 features:

d3.tsv - load and parse data

d3.format - format percentages

d3.scale.ordinal - x-position encoding

d3.scale.linear - y-position encoding

d3.max - compute domains

d3.svg.axis - display axes

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<!DOCTYPE html>
<meta charset="utf-8">
<style>
​
.bar {
  fill: steelblue;
}
​
.bar:hover {
  fill: darkblue;
}
​
.axis {
  font: 10px sans-serif;
}
​
.axis path,
.axis line {
  fill: none;
  stroke: #000;
  shape-rendering: crispEdges;
}
​
.x.axis path {
  display: none;
}
​
</style>
<body>
<script src="//d3js.org/d3.v3.min.js"></script>
<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;
​
var x = d3.scale.ordinal()
    .rangeRoundBands([0, width], 0.1);
​
var y = d3.scale.linear()
    .range([height, 0]);
​
var xAxis = d3.svg.axis()
    .scale(x)
    .orient("bottom");
​
var yAxis = d3.svg.axis()
    .scale(y)
    .orient("left")
    .ticks(10);
​
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 + ")");
​
d3.tsv("data.tsv", type, function(error, data) {
  x.domain(data.map(function(d) { 
    return d.code; }));
  y.domain([0, d3.max(data, function(d) { 
    return d.grade; })]);
  
   data.sort(function(a, b) {
    return a.code - b.code;
  });
  
   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", "0.71em")
      .style("text-anchor", "middle")
      .text("Grade Scale");
​
  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); });
});
​
function type(d) {
  d.grade = +d.grade;
  return d;
}
​
</script>
​
    