Cluster tree

D3’s cluster layout produces node-link diagrams with leaf nodes at equal depth. These are less compact than tidy trees, but are useful for dendrograms, hierarchical clustering, and phylogenetic trees. See also the radial variant.

const width = 960;

// Compute the tree height; this approach will allow the height of the
// SVG to scale according to the breadth (width) of the tree layout.
const root = d3.hierarchy(data);
const dx = 10;
const dy = width / (root.height + 1);

// Create a tree layout.
const tree = d3.cluster().nodeSize([dx, dy]);

// Sort the tree and apply the layout.
root.sort((a, b) => d3.ascending(a.data.name, b.data.name));
tree(root);

// Compute the extent of the tree. Note that x and y are swapped here
// because in the tree layout, x is the breadth, but when displayed, the
// tree extends right rather than down.
let x0 = Infinity;
let x1 = -x0;
root.each((d) => {
  if (d.x > x1) x1 = d.x;
  if (d.x < x0) x0 = d.x;
});

// Compute the adjusted height of the tree.
const height = x1 - x0 + dx * 2;

const svg = d3.create("svg")
    .attr("width", width)
    .attr("height", height)
    .attr("viewBox", [-dy / 3, x0 - dx, width, height])
    .attr("style", "max-width: 100%; height: auto; font: 10px sans-serif;");

const link = svg.append("g")
    .attr("fill", "none")
    .attr("stroke", "#555")
    .attr("stroke-opacity", 0.4)
    .attr("stroke-width", 1.5)
  .selectAll()
    .data(root.links())
    .join("path")
      .attr("d", d3.linkHorizontal()
          .x((d) => d.y)
          .y((d) => d.x));

const node = svg.append("g")
    .attr("stroke-linejoin", "round")
    .attr("stroke-width", 3)
  .selectAll()
  .data(root.descendants())
  .join("g")
    .attr("transform", (d) => `translate(${d.y},${d.x})`);

node.append("circle")
    .attr("fill", (d) => d.children ? "#555" : "#999")
    .attr("r", 2.5);

node.append("text")
    .attr("dy", "0.31em")
    .attr("x", (d) => d.children ? -6 : 6)
    .attr("text-anchor", (d) => d.children ? "end" : "start")
    .text((d) => d.data.name)
    .attr("stroke", "white")
    .attr("paint-order", "stroke");

display(svg.node());

const data = FileAttachment("data/flare.json").json().then(display);