Dots colored by a property named group.
Dots can be dragged like in my Draggable dots block.
forked from mbostock's block: Collision Detection
with code from mbostock's block: Multi-Foci Force Layout
forked from ocarneiro's block: Grouped dots
forked from ocarneiro's block: simple group d3 v4
forked from shimizu's block: D3 v4 - force layout
https://d3js.org/d3.v4.min.js