Parallel Coordinates

This parallel coordinates visualization of cars from the ‘70s and ‘80s demonstrates one of D3 2.5.0’s new interactive features: the brush component. By clicking and dragging along any axis, you can specify a filter for that dimension. The brush component is also used in the updated scatterplot matrix example.

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

svg {
  font: 10px sans-serif;
}

.background path {
  fill: none;
  stroke: #ccc;
  stroke-opacity: .4;
  shape-rendering: crispEdges;
}

.foreground path {
  fill: none;
  stroke: steelblue;
  stroke-opacity: .7;
}

.brush .extent {
  fill-opacity: .3;
  stroke: #fff;
  shape-rendering: crispEdges;
}

.axis line,
.axis path {
  fill: none;
  stroke: #000;
  shape-rendering: crispEdges;
}

.axis text {
  text-shadow: 0 1px 0 #fff;
  cursor: move;
}

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

var m = [30, 10, 10, 10],
    w = 960 - m[1] - m[3],
    h = 500 - m[0] - m[2];

var x = d3.scale.ordinal().rangePoints([0, w], 1),
    y = {},
    dragging = {};

var line = d3.svg.line(),
    axis = d3.svg.axis().orient("left"),
    background,
    foreground;

var svg = d3.select("body").append("svg")
    .attr("width", w + m[1] + m[3])
    .attr("height", h + m[0] + m[2])
  .append("g")
    .attr("transform", "translate(" + m[3] + "," + m[0] + ")");

d3.csv("cars.csv", function(error, cars) {

// Extract the list of dimensions and create a scale for each.
  x.domain(dimensions = d3.keys(cars[0]).filter(function(d) {
    return d != "name" && (y[d] = d3.scale.linear()
        .domain(d3.extent(cars, function(p) { return +p[d]; }))
        .range([h, 0]));
  }));

// Add grey background lines for context.
  background = svg.append("g")
      .attr("class", "background")
    .selectAll("path")
      .data(cars)
    .enter().append("path")
      .attr("d", path);

// Add blue foreground lines for focus.
  foreground = svg.append("g")
      .attr("class", "foreground")
    .selectAll("path")
      .data(cars)
    .enter().append("path")
      .attr("d", path);

// Add a group element for each dimension.
  var g = svg.selectAll(".dimension")
      .data(dimensions)
    .enter().append("g")
      .attr("class", "dimension")
      .attr("transform", function(d) { return "translate(" + x(d) + ")"; })
      .call(d3.behavior.drag()
        .on("dragstart", function(d) {
          dragging[d] = this.__origin__ = x(d);
          background.attr("visibility", "hidden");
        })
        .on("drag", function(d) {
          dragging[d] = Math.min(w, Math.max(0, this.__origin__ += d3.event.dx));
          foreground.attr("d", path);
          dimensions.sort(function(a, b) { return position(a) - position(b); });
          x.domain(dimensions);
          g.attr("transform", function(d) { return "translate(" + position(d) + ")"; })
        })
        .on("dragend", function(d) {
          delete this.__origin__;
          delete dragging[d];
          transition(d3.select(this)).attr("transform", "translate(" + x(d) + ")");
          transition(foreground)
              .attr("d", path);
          background
              .attr("d", path)
              .transition()
              .delay(500)
              .duration(0)
              .attr("visibility", null);
        }));

// Add an axis and title.
  g.append("g")
      .attr("class", "axis")
      .each(function(d) { d3.select(this).call(axis.scale(y[d])); })
    .append("text")
      .attr("text-anchor", "middle")
      .attr("y", -9)
      .text(String);

// Add and store a brush for each axis.
  g.append("g")
      .attr("class", "brush")
      .each(function(d) { d3.select(this).call(y[d].brush = d3.svg.brush().y(y[d]).on("brushstart", brushstart).on("brush", brush)); })
    .selectAll("rect")
      .attr("x", -8)
      .attr("width", 16);
});

function position(d) {
  var v = dragging[d];
  return v == null ? x(d) : v;
}

function transition(g) {
  return g.transition().duration(500);
}

// Returns the path for a given data point.
function path(d) {
  return line(dimensions.map(function(p) { return [position(p), y[p](d[p])]; }));
}

// When brushing, don’t trigger axis dragging.
function brushstart() {
  d3.event.sourceEvent.stopPropagation();
}

// Handles a brush event, toggling the display of foreground lines.
function brush() {
  var actives = dimensions.filter(function(p) { return !y[p].brush.empty(); }),
      extents = actives.map(function(p) { return y[p].brush.extent(); });
  foreground.style("display", function(d) {
    return actives.every(function(p, i) {
      return extents[i][0] <= d[p] && d[p] <= extents[i][1];
    }) ? null : "none";
  });
}

</script>

https://d3js.org/d3.v3.min.js