d3.json("flowers.json", function(flower) {

  // Size parameters.

  var size = 150,

      padding = 19.5,

      n = flower.traits.length;

  // Position scales.

  var x = {}, y = {};

  flower.traits.forEach(function(trait) {

    var value = function(d) { return d[trait]; },

        domain = [d3.min(flower.values, value), d3.max(flower.values, value)],

        range = [padding / 2, size - padding / 2];

    x[trait] = d3.scale.linear().domain(domain).range(range);

    y[trait] = d3.scale.linear().domain(domain).range(range.reverse());

  });

  // Axes.

  var axis = d3.svg.axis()

      .ticks(5)

      .tickSize(size * n);

  // Brush.

  var brush = d3.svg.brush()

      .on("brushstart", brushstart)

      .on("brush", brush)

      .on("brushend", brushend);

  // Root panel.

  var svg = d3.select("#chart").append("svg:svg")

      .attr("width", size * n + padding)

      .attr("height", size * n + padding);

  // X-axis.

  svg.selectAll("g.x.axis")

      .data(flower.traits)

    .enter().append("svg:g")

      .attr("class", "x axis")

      .attr("transform", function(d, i) { return "translate(" + i * size + ",0)"; })

      .each(function(d) { d3.select(this).call(axis.scale(x[d]).orient("bottom")); });

  // Y-axis.

  svg.selectAll("g.y.axis")

      .data(flower.traits)

    .enter().append("svg:g")

      .attr("class", "y axis")

      .attr("transform", function(d, i) { return "translate(0," + i * size + ")"; })

      .each(function(d) { d3.select(this).call(axis.scale(y[d]).orient("right")); });

  // Cell and plot.

  var cell = svg.selectAll("g.cell")

      .data(cross(flower.traits, flower.traits))

    .enter().append("svg:g")

      .attr("class", "cell")

      .attr("transform", function(d) { return "translate(" + d.i * size + "," + d.j * size + ")"; })

      .each(plot);

  // Titles for the diagonal.

  cell.filter(function(d) { return d.i == d.j; }).append("svg:text")

      .attr("x", padding)

      .attr("y", padding)

      .attr("dy", ".71em")

      .text(function(d) { return d.x; });

  function plot(p) {

    var cell = d3.select(this);

    // Plot frame.

    cell.append("svg:rect")

        .attr("class", "frame")

        .attr("x", padding / 2)

        .attr("y", padding / 2)

        .attr("width", size - padding)

        .attr("height", size - padding);

    // Plot dots.

    cell.selectAll("circle")

        .data(flower.values)

      .enter().append("svg:circle")

        .attr("class", function(d) { return d.species; })

        .attr("cx", function(d) { return x[p.x](d[p.x]); })

        .attr("cy", function(d) { return y[p.y](d[p.y]); })

        .attr("r", 3);

    // Plot brush.

    cell.call(brush.x(x[p.x]).y(y[p.y]));

  }

  // Clear the previously-active brush, if any.

  function brushstart(p) {

    if (brush.data !== p) {

      cell.call(brush.clear());

      brush.x(x[p.x]).y(y[p.y]).data = p;

    }

  }

  // Highlight the selected circles.

  function brush(p) {

    var e = brush.extent();

    svg.selectAll("circle").attr("class", function(d) {

      return e[0][0] <= d[p.x] && d[p.x] < e[1][0]

          && e[0][1] <= d[p.y] && d[p.y] < e[1][1]

          ? d.species : null;

    });

  }

  // If the brush is empty, select all circles.

  function brushend() {

    if (brush.empty()) svg.selectAll("circle").attr("class", function(d) {

      return d.species;

    });

  }

  function cross(a, b) {

    var c = [], n = a.length, m = b.length, i, j;

    for (i = -1; ++i < n;) for (j = -1; ++j < m;) c.push({x: a[i], i: i, y: b[j], j: j});

    return c;

  }

});