add clustering force

src/cluster.js

@@ -0,0 +1,65 @@
+import jiggle from "./jiggle.js";
+
+function group(d) {
+  return d.group;
+}
+
+export default function (groups) {
+  var id = group,
+      strength = 0.5,
+      radius = 10,
+      nodes;
+
+  if (groups == null) groups = [];
+
+  function force(alpha) {
+    groups.forEach((c) => {
+      const avg = c.nodes.reduce((o, n) => ({
+        x: o.x + (n.x || 0),
+        y: o.y + (n.y || 0)
+      }), {x: 0, y: 0});
+
+      c.x = c.fx ? c.fx : avg.x / c.nodes.length;
+      c.y = c.fy ? c.fy : avg.y / c.nodes.length;
+
+      c.nodes.forEach((n) => {
+        let x = (n.x - c.x) || jiggle(),
+            y = (n.y - c.y) || jiggle(),
+            l = Math.hypot(x, y);
+        l = strength * alpha * (l - radius) / l;
+        n.vx -= x * l;
+        n.vy -= y * l;
+      });
+    });
+  }
+
+  function init() {
+    if (!nodes) return;
+    groups.forEach((c) => {
+      c.nodes = nodes.filter((n) => id(n) === c.id)
+    })
+  }
+
+  force.initialize = function(_) {
+    nodes = _;
+    init();
+  };
+
+  force.id = function(_) {
+    return arguments.length ? (id = _, force) : id;
+  };
+
+  force.groups = function(_) {
+    return arguments.length ? (groups = _, init(), force) : groups;
+  };
+
+  force.strength = function(_) {
+    return arguments.length ? (strength = +_, force) : strength;
+  };
+
+  force.radius = function(_) {
+    return arguments.length ? (radius = +_, force) : radius;
+  };
+
+  return force;
+}

src/index.js

@@ -2,6 +2,7 @@ export {default as forceCenter} from "./center.js";
 export {default as forceCollide} from "./collide.js";
 export {default as forceLink} from "./link.js";
 export {default as forceManyBody} from "./manyBody.js";
+export {default as forceCluster} from "./cluster.js";
 export {default as forceRadial} from "./radial.js";
 export {default as forceSimulation} from "./simulation.js";
 export {default as forceX} from "./x.js";