D3 v4 forcelayout example with dropdown filters.
forked from mbostock's block: Force Dragging I
forked from almsuarez's block: Force Layout v4 with Filters
forked from almsuarez's block: Force Layout v4 with Filters v2
forked from almsuarez's block: (d3v4) Force Layout w highlights
https://d3js.org/d3.v4.min.js
https://cdnjs.cloudflare.com/ajax/libs/d3-legend/2.24.0/d3-legend.min.js
https://d3js.org/d3-scale-chromatic.v1.min.js