sort.js

customChordLayout = function() {
	var ε = 1e-6, ε2 = ε * ε, π = Math.PI, τ = 2 * π, τε = τ - ε, halfπ = π / 2, d3_radians = π / 180, d3_degrees = 180 / π;
    var chord = {}, chords, groups, matrix, n, padding = 0, sortGroups, sortSubgroups, sortChords;
    function relayout() {
      var subgroups = {}, groupSums = [], groupIndex = d3.range(n), subgroupIndex = [], k, x, x0, i, j;
      chords = [];
      groups = [];
      k = 0, i = -1;
      while (++i < n) {
        x = 0, j = -1;
        while (++j < n) {
          x += matrix[i][j];
        }
        groupSums.push(x);
        subgroupIndex.push(d3.range(n).reverse());
        k += x;
      }
      if (sortGroups) {
        groupIndex.sort(function(a, b) {
          return sortGroups(groupSums[a], groupSums[b]);
        });
      }
      if (sortSubgroups) {
        subgroupIndex.forEach(function(d, i) {
          d.sort(function(a, b) {
            return sortSubgroups(matrix[i][a], matrix[i][b]);
          });
        });
      }
      k = (τ - padding * n) / k;
      x = 0, i = -1;
      while (++i < n) {
        x0 = x, j = -1;
        while (++j < n) {
          var di = groupIndex[i], dj = subgroupIndex[di][j], v = matrix[di][dj], a0 = x, a1 = x += v * k;
          subgroups[di + "-" + dj] = {
            index: di,
            subindex: dj,
            startAngle: a0,
            endAngle: a1,
            value: v
          };
        }
        groups[di] = {
          index: di,
          startAngle: x0,
          endAngle: x,
          value: (x - x0) / k
        };
        x += padding;
      }
      i = -1;
      while (++i < n) {
        j = i - 1;
        while (++j < n) {
          var source = subgroups[i + "-" + j], target = subgroups[j + "-" + i];
          if (source.value || target.value) {
            chords.push(source.value < target.value ? {
              source: target,
              target: source
            } : {
              source: source,
              target: target
            });
          }
        }
      }
      if (sortChords) resort();
    }
    function resort() {
      chords.sort(function(a, b) {
        return sortChords((a.source.value + a.target.value) / 2, (b.source.value + b.target.value) / 2);
      });
    }
    chord.matrix = function(x) {
      if (!arguments.length) return matrix;
      n = (matrix = x) && matrix.length;
      chords = groups = null;
      return chord;
    };
    chord.padding = function(x) {
      if (!arguments.length) return padding;
      padding = x;
      chords = groups = null;
      return chord;
    };
    chord.sortGroups = function(x) {
      if (!arguments.length) return sortGroups;
      sortGroups = x;
      chords = groups = null;
      return chord;
    };
    chord.sortSubgroups = function(x) {
      if (!arguments.length) return sortSubgroups;
      sortSubgroups = x;
      chords = null;
      return chord;
    };
    chord.sortChords = function(x) {
      if (!arguments.length) return sortChords;
      sortChords = x;
      if (chords) resort();
      return chord;
    };
    chord.chords = function() {
      if (!chords) relayout();
      return chords;
    };
    chord.groups = function() {
      if (!groups) relayout();
      return groups;
    };
    return chord;
  };