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.

Update: Jason Davies has derived an example with reorderable axes!

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

svg {
  font: 10px sans-serif;
}

.background path {
  fill: none;
  stroke: #ddd;
  shape-rendering: crispEdges;
}

.foreground path {
  fill: none;
  stroke: steelblue;
}

.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, 1px 0 0 #fff, 0 -1px 0 #fff, -1px 0 0 #fff;
}

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

var margin = {top: 30, right: 10, bottom: 10, left: 10},
    width = 960 - margin.left - margin.right,
    height = 500 - margin.top - margin.bottom;

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

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

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.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([height, 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) + ")"; });

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

// 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("brush", brush)); })
    .selectAll("rect")
      .attr("x", -8)
      .attr("width", 16);
});

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

// 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