Old school D3 from simpler times
Clustered Force Layout I
This clustered force layout is implemented using two custom forces. The first,
cluster, pushes nodes towards the largest node of the same color. A second
collide force prevents circles from overlapping by detecting collisions.
This example uses standard gravity; compare to custom gravity applied only to the largest node of each color. To minimize distracting jitter during initialization, try an entry transition.