D3.js Code for Bullet Charts

Understand the code for bullet charts and learn how to create bullet charts in D3.

We'll cover the following...

We’ll move through the explanation of the code in a similar process to the other examples in the course. Where there are areas that we have covered before, I will gloss over some details on the understanding that you will have already seen them explained in an earlier section (most likely the basic line graph example).

The code

Here is the full code:

(function() {

// Chart design based on the recommendations of Stephen Few. Implementation
// based on the work of Clint Ivy, Jamie Love, and Jason Davies.
// http://projects.instantcognition.com/protovis/bulletchart/
d3.bullet = function() {
  var orient = "left", // TODO top & bottom
      reverse = false,
      duration = 0,
      ranges = bulletRanges,
      markers = bulletMarkers,
      measures = bulletMeasures,
      width = 380,
      height = 30,
      tickFormat = d3.format(",.1f");

  // For each small multiple…
  function bullet(g) {
    g.each(function(d, i) {
      var rangez = ranges.call(this, d, i).slice().sort(d3.descending),
          markerz = markers.call(this, d, i).slice().sort(d3.descending),
          measurez = measures.call(this, d, i).slice().sort(d3.descending),
          g = d3.select(this);

      // Compute the new x-scale.
      var x1 = d3.scaleLinear()
          .domain([0, Math.max(rangez[0], markerz[0], measurez[0])])
          .range(reverse ? [width, 0] : [0, width]);

      // Retrieve the old x-scale, if this is an update.
      var x0 = this.__chart__ || d3.scaleLinear()
          .domain([0, Infinity])
          .range(x1.range());

      // Stash the new scale.
      this.__chart__ = x1;

      // Derive width-scales from the x-scales.
      var w0 = bulletWidth(x0),
          w1 = bulletWidth(x1);

      // Update the range rects.
      var range = g.selectAll("rect.range")
          .data(rangez);

      range.enter().append("rect")
          .attr("class", function(d, i) { return "range s" + i; })
          .attr("width", w0)
          .attr("height", height)
          .attr("x", reverse ? x0 : 0)
        .transition()
          .duration(duration)
          .attr("width", w1)
          .attr("x", reverse ? x1 : 0);

      range.transition()
          .duration(duration)
          .attr("x", reverse ? x1 : 0)
          .attr("width", w1)
          .attr("height", height);

      // Update the measure rects.
      var measure = g.selectAll("rect.measure")
          .data(measurez);

      measure.enter().append("rect")
          .attr("class", function(d, i) { return "measure s" + i; })
          .attr("width", w0)
          .attr("height", height / 3)
          .attr("x", reverse ? x0 : 0)
          .attr("y", height / 3)
        .transition()
          .duration(duration)
          .attr("width", w1)
          .attr("x", reverse ? x1 : 0);

      measure.transition()
          .duration(duration)
          .attr("width", w1)
          .attr("height", height / 3)
          .attr("x", reverse ? x1 : 0)
          .attr("y", height / 3);

      // Update the marker lines.
      var marker = g.selectAll("line.marker")
          .data(markerz);

      marker.enter().append("line")
          .attr("class", "marker")
          .attr("x1", x0)
          .attr("x2", x0)
          .attr("y1", height / 6)
          .attr("y2", height * 5 / 6)
        .transition()
          .duration(duration)
          .attr("x1", x1)
          .attr("x2", x1);

      marker.transition()
          .duration(duration)
          .attr("x1", x1)
          .attr("x2", x1)
          .attr("y1", height / 6)
          .attr("y2", height * 5 / 6);

      // Compute the tick format.
      var format = tickFormat || x1.tickFormat(8);

      // Update the tick groups.
      var tick = g.selectAll("g.tick")
          .data(x1.ticks(8), function(d) {
            return this.textContent || format(d);
          });

      // Initialize the ticks with the old scale, x0.
      var tickEnter = tick.enter().append("g")
          .attr("class", "tick")
          .attr("transform", bulletTranslate(x0))
          .style("opacity", 1e-6);

      tickEnter.append("line")
          .attr("y1", height)
          .attr("y2", height * 7 / 6);

      tickEnter.append("text")
          .attr("text-anchor", "middle")
          .attr("dy", "1em")
          .attr("y", height * 7 / 6)
          .text(format);

      // Transition the entering ticks to the new scale, x1.
      tickEnter.transition()
          .duration(duration)
          .attr("transform", bulletTranslate(x1))
          .style("opacity", 1);

      // Transition the updating ticks to the new scale, x1.
      var tickUpdate = tick.transition()
          .duration(duration)
          .attr("transform", bulletTranslate(x1))
          .style("opacity", 1);

      tickUpdate.select("line")
          .attr("y1", height)
          .attr("y2", height * 7 / 6);

      tickUpdate.select("text")
          .attr("y", height * 7 / 6);

      // Transition the exiting ticks to the new scale, x1.
      tick.exit().transition()
          .duration(duration)
          .attr("transform", bulletTranslate(x1))
          .style("opacity", 1e-6)
          .remove();
    });
    //d3.timer.flush();
  }

  // left, right, top, bottom
  bullet.orient = function(x) {
    if (!arguments.length) return orient;
    orient = x;
    reverse = orient == "right" || orient == "bottom";
    return bullet;
  };

  // ranges (bad, satisfactory, good)
  bullet.ranges = function(x) {
    if (!arguments.length) return ranges;
    ranges = x;
    return bullet;
  };

  // markers (previous, goal)
  bullet.markers = function(x) {
    if (!arguments.length) return markers;
    markers = x;
    return bullet;
  };

  // measures (actual, forecast)
  bullet.measures = function(x) {
    if (!arguments.length) return measures;
    measures = x;
    return bullet;
  };

  bullet.width = function(x) {
    if (!arguments.length) return width;
    width = x;
    return bullet;
  };

  bullet.height = function(x) {
    if (!arguments.length) return height;
    height = x;
    return bullet;
  };

  bullet.tickFormat = function(x) {
    if (!arguments.length) return tickFormat;
    tickFormat = x;
    return bullet;
  };

  bullet.duration = function(x) {
    if (!arguments.length) return duration;
    duration = x;
    return bullet;
  };

  return bullet;
};

function bulletRanges(d) {
  return d.ranges;
}

function bulletMarkers(d) {
  return d.markers;
}

function bulletMeasures(d) {
  return d.measures;
}

function bulletTranslate(x) {
  return function(d) {
    return "translate(" + x(d) + ",0)";
  };
}

function bulletWidth(x) {
  var x0 = x(0);
  return function(d) {
    return Math.abs(x(d) - x0);
  };
}

})();
Bullet chart code

It will become clearer in the process of going through the code below, but as a teaser, it is worth noting that while the code that we will modify is as presented above, we are employing a separate script bullet.js to enable the charts.

Explanation

Lines 1-3: The first block of our code is the start of the file and sets up our HTML.

Lines 5-27: This leads to our style declarations.

  • We declare the (general) styling for the chart page in the first instance and then the button. Then we move on to the more interesting styling for the bullet charts.

  • The first line (line 19) .bullet { font: 10px sans-serif; } sets the font size.

  • The second line (line 20) sets the color and width of the symbol ...