Force-directed graph

const height = 600;
const color = d3.scaleOrdinal(d3.schemeObservable10);

// Make a copy prior to mutation.
const links = data.links.map((d) => structuredClone(d));
const nodes = data.nodes.map((d) => structuredClone(d));

const simulation = d3.forceSimulation(nodes)
    .force("link", d3.forceLink(links).id((d) => d.id))
    .force("charge", d3.forceManyBody())
    .force("center", d3.forceCenter(width / 2, height / 2));

const svg = d3.create("svg")
    .attr("viewBox", [0, 0, width, height]);

const link = svg.append("g")
    .attr("stroke", "#999")
    .attr("stroke-opacity", 0.6)
  .selectAll("line")
  .data(links)
  .join("line")
    .attr("stroke-width", (d) => Math.sqrt(d.value));

const node = svg.append("g")
    .attr("stroke", "#fff")
    .attr("stroke-width", 1.5)
  .selectAll("circle")
  .data(nodes)
  .join("circle")
    .attr("r", 5)
    .attr("fill", (d) => color(d.group))
    .call(drag(simulation));

node.append("title")
    .text((d) => d.id);

simulation.on("tick", () => {
  link
      .attr("x1", (d) => d.source.x)
      .attr("y1", (d) => d.source.y)
      .attr("x2", (d) => d.target.x)
      .attr("y2", (d) => d.target.y);

  node
      .attr("cx", (d) => d.x)
      .attr("cy", (d) => d.y);
});

invalidation.then(() => simulation.stop());

display(svg.node());

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

function drag(simulation) {

  function dragstarted(event) {
    if (!event.active) simulation.alphaTarget(0.3).restart();
    event.subject.fx = event.subject.x;
    event.subject.fy = event.subject.y;
  }

  function dragged(event) {
    event.subject.fx = event.x;
    event.subject.fy = event.y;
  }

  function dragended(event) {
    if (!event.active) simulation.alphaTarget(0);
    event.subject.fx = null;
    event.subject.fy = null;
  }

  return d3.drag()
      .on("start", dragstarted)
      .on("drag", dragged)
      .on("end", dragended);
}