Box Plots

.block

license: gpl-3.0

README.md

A box-and-whisker plot uses simple glyphs that summarize a quantitative distribution with five standard statistics: the smallest value, lower quartile, median, upper quartile, and largest value. This summary approach allows the viewer to easily recognize differences between distributions. Data from the Michelson–Morley experiment. Implementation contributed by Jason Davies. This example periodically randomizes the values to demonstrate transitions.

box.js

(function() {

// Inspired by http://informationandvisualization.de/blog/box-plot
d3.box = function() {
  var width = 1,
      height = 1,
      duration = 0,
      domain = null,
      value = Number,
      whiskers = boxWhiskers,
      quartiles = boxQuartiles,
      tickFormat = null;

  // For each small multiple…
  function box(g) {
    g.each(function(d, i) {
      d = d.map(value).sort(d3.ascending);
      var g = d3.select(this),
          n = d.length,
          min = d[0],
          max = d[n - 1];

      // Compute quartiles. Must return exactly 3 elements.
      var quartileData = d.quartiles = quartiles(d);

      // Compute whiskers. Must return exactly 2 elements, or null.
      var whiskerIndices = whiskers && whiskers.call(this, d, i),
          whiskerData = whiskerIndices && whiskerIndices.map(function(i) { return d[i]; });

      // Compute outliers. If no whiskers are specified, all data are "outliers".
      // We compute the outliers as indices, so that we can join across transitions!
      var outlierIndices = whiskerIndices
          ? d3.range(0, whiskerIndices[0]).concat(d3.range(whiskerIndices[1] + 1, n))
          : d3.range(n);

      // Compute the new x-scale.
      var x1 = d3.scale.linear()
          .domain(domain && domain.call(this, d, i) || [min, max])
          .range([height, 0]);

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

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

      // Note: the box, median, and box tick elements are fixed in number,
      // so we only have to handle enter and update. In contrast, the outliers
      // and other elements are variable, so we need to exit them! Variable
      // elements also fade in and out.

      // Update center line: the vertical line spanning the whiskers.
      var center = g.selectAll("line.center")
          .data(whiskerData ? [whiskerData] : []);

      center.enter().insert("line", "rect")
          .attr("class", "center")
          .attr("x1", width / 2)
          .attr("y1", function(d) { return x0(d[0]); })
          .attr("x2", width / 2)
          .attr("y2", function(d) { return x0(d[1]); })
          .style("opacity", 1e-6)
        .transition()
          .duration(duration)
          .style("opacity", 1)
          .attr("y1", function(d) { return x1(d[0]); })
          .attr("y2", function(d) { return x1(d[1]); });

      center.transition()
          .duration(duration)
          .style("opacity", 1)
          .attr("y1", function(d) { return x1(d[0]); })
          .attr("y2", function(d) { return x1(d[1]); });

      center.exit().transition()
          .duration(duration)
          .style("opacity", 1e-6)
          .attr("y1", function(d) { return x1(d[0]); })
          .attr("y2", function(d) { return x1(d[1]); })
          .remove();

      // Update innerquartile box.
      var box = g.selectAll("rect.box")
          .data([quartileData]);

      box.enter().append("rect")
          .attr("class", "box")
          .attr("x", 0)
          .attr("y", function(d) { return x0(d[2]); })
          .attr("width", width)
          .attr("height", function(d) { return x0(d[0]) - x0(d[2]); })
        .transition()
          .duration(duration)
          .attr("y", function(d) { return x1(d[2]); })
          .attr("height", function(d) { return x1(d[0]) - x1(d[2]); });

      box.transition()
          .duration(duration)
          .attr("y", function(d) { return x1(d[2]); })
          .attr("height", function(d) { return x1(d[0]) - x1(d[2]); });

      // Update median line.
      var medianLine = g.selectAll("line.median")
          .data([quartileData[1]]);

      medianLine.enter().append("line")
          .attr("class", "median")
          .attr("x1", 0)
          .attr("y1", x0)
          .attr("x2", width)
          .attr("y2", x0)
        .transition()
          .duration(duration)
          .attr("y1", x1)
          .attr("y2", x1);

      medianLine.transition()
          .duration(duration)
          .attr("y1", x1)
          .attr("y2", x1);

      // Update whiskers.
      var whisker = g.selectAll("line.whisker")
          .data(whiskerData || []);

      whisker.enter().insert("line", "circle, text")
          .attr("class", "whisker")
          .attr("x1", 0)
          .attr("y1", x0)
          .attr("x2", width)
          .attr("y2", x0)
          .style("opacity", 1e-6)
        .transition()
          .duration(duration)
          .attr("y1", x1)
          .attr("y2", x1)
          .style("opacity", 1);

      whisker.transition()
          .duration(duration)
          .attr("y1", x1)
          .attr("y2", x1)
          .style("opacity", 1);

      whisker.exit().transition()
          .duration(duration)
          .attr("y1", x1)
          .attr("y2", x1)
          .style("opacity", 1e-6)
          .remove();

      // Update outliers.
      var outlier = g.selectAll("circle.outlier")
          .data(outlierIndices, Number);

      outlier.enter().insert("circle", "text")
          .attr("class", "outlier")
          .attr("r", 5)
          .attr("cx", width / 2)
          .attr("cy", function(i) { return x0(d[i]); })
          .style("opacity", 1e-6)
        .transition()
          .duration(duration)
          .attr("cy", function(i) { return x1(d[i]); })
          .style("opacity", 1);

      outlier.transition()
          .duration(duration)
          .attr("cy", function(i) { return x1(d[i]); })
          .style("opacity", 1);

      outlier.exit().transition()
          .duration(duration)
          .attr("cy", function(i) { return x1(d[i]); })
          .style("opacity", 1e-6)
          .remove();

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

      // Update box ticks.
      var boxTick = g.selectAll("text.box")
          .data(quartileData);

      boxTick.enter().append("text")
          .attr("class", "box")
          .attr("dy", ".3em")
          .attr("dx", function(d, i) { return i & 1 ? 6 : -6 })
          .attr("x", function(d, i) { return i & 1 ? width : 0 })
          .attr("y", x0)
          .attr("text-anchor", function(d, i) { return i & 1 ? "start" : "end"; })
          .text(format)
        .transition()
          .duration(duration)
          .attr("y", x1);

      boxTick.transition()
          .duration(duration)
          .text(format)
          .attr("y", x1);

      // Update whisker ticks. These are handled separately from the box
      // ticks because they may or may not exist, and we want don't want
      // to join box ticks pre-transition with whisker ticks post-.
      var whiskerTick = g.selectAll("text.whisker")
          .data(whiskerData || []);

      whiskerTick.enter().append("text")
          .attr("class", "whisker")
          .attr("dy", ".3em")
          .attr("dx", 6)
          .attr("x", width)
          .attr("y", x0)
          .text(format)
          .style("opacity", 1e-6)
        .transition()
          .duration(duration)
          .attr("y", x1)
          .style("opacity", 1);

      whiskerTick.transition()
          .duration(duration)
          .text(format)
          .attr("y", x1)
          .style("opacity", 1);

      whiskerTick.exit().transition()
          .duration(duration)
          .attr("y", x1)
          .style("opacity", 1e-6)
          .remove();
    });
    d3.timer.flush();
  }

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

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

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

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

  box.domain = function(x) {
    if (!arguments.length) return domain;
    domain = x == null ? x : d3.functor(x);
    return box;
  };

  box.value = function(x) {
    if (!arguments.length) return value;
    value = x;
    return box;
  };

  box.whiskers = function(x) {
    if (!arguments.length) return whiskers;
    whiskers = x;
    return box;
  };

  box.quartiles = function(x) {
    if (!arguments.length) return quartiles;
    quartiles = x;
    return box;
  };

  return box;
};

function boxWhiskers(d) {
  return [0, d.length - 1];
}

function boxQuartiles(d) {
  return [
    d3.quantile(d, .25),
    d3.quantile(d, .5),
    d3.quantile(d, .75)
  ];
}

})();

index.html

<!DOCTYPE html>
<meta charset="utf-8">
<style>

body {
  font-family: "Helvetica Neue", Helvetica, Arial, sans-serif;
}

.box {
  font: 10px sans-serif;
}

.box line,
.box rect,
.box circle {
  fill: #fff;
  stroke: #000;
  stroke-width: 1.5px;
}

.box .center {
  stroke-dasharray: 3,3;
}

.box .outlier {
  fill: none;
  stroke: #ccc;
}

</style>
<body>
<script src="//d3js.org/d3.v3.min.js"></script>
<script src="box.js"></script>
<script>

var margin = {top: 10, right: 50, bottom: 20, left: 50},
    width = 120 - margin.left - margin.right,
    height = 500 - margin.top - margin.bottom;

var min = Infinity,
    max = -Infinity;

var chart = d3.box()
    .whiskers(iqr(1.5))
    .width(width)
    .height(height);

d3.csv("morley.csv", function(error, csv) {
  if (error) throw error;

  var data = [];

  csv.forEach(function(x) {
    var e = Math.floor(x.Expt - 1),
        r = Math.floor(x.Run - 1),
        s = Math.floor(x.Speed),
        d = data[e];
    if (!d) d = data[e] = [s];
    else d.push(s);
    if (s > max) max = s;
    if (s < min) min = s;
  });

  chart.domain([min, max]);

  var svg = d3.select("body").selectAll("svg")
      .data(data)
    .enter().append("svg")
      .attr("class", "box")
      .attr("width", width + margin.left + margin.right)
      .attr("height", height + margin.bottom + margin.top)
    .append("g")
      .attr("transform", "translate(" + margin.left + "," + margin.top + ")")
      .call(chart);

  setInterval(function() {
    svg.datum(randomize).call(chart.duration(1000));
  }, 2000);
});

function randomize(d) {
  if (!d.randomizer) d.randomizer = randomizer(d);
  return d.map(d.randomizer);
}

function randomizer(d) {
  var k = d3.max(d) * .02;
  return function(d) {
    return Math.max(min, Math.min(max, d + k * (Math.random() - .5)));
  };
}

// Returns a function to compute the interquartile range.
function iqr(k) {
  return function(d, i) {
    var q1 = d.quartiles[0],
        q3 = d.quartiles[2],
        iqr = (q3 - q1) * k,
        i = -1,
        j = d.length;
    while (d[++i] < q1 - iqr);
    while (d[--j] > q3 + iqr);
    return [i, j];
  };
}

</script>

morley.csv

thumbnail.png