This example shows how it is possible to use crossfilter bar charts (up to any number) to visually subset a choropleth. The map above shows the population and per-capita income growth of the US from 2011-2012.
Modified http://d3js.org/d3.v3.min.js to a secure url
Modified http://d3js.org/queue.v1.min.js to a secure url
Modified http://d3js.org/topojson.v1.min.js to a secure url
Modified http://cdnjs.cloudflare.com/ajax/libs/crossfilter/1.3.1/crossfilter.min.js to a secure url
Modified http://labratrevenge.com/d3-tip/javascripts/d3.tip.v0.6.3.js to a secure url
https://d3js.org/d3.v3.min.js
https://d3js.org/queue.v1.min.js
https://d3js.org/topojson.v1.min.js
https://cdnjs.cloudflare.com/ajax/libs/crossfilter/1.3.1/crossfilter.min.js
https://labratrevenge.com/d3-tip/javascripts/d3.tip.v0.6.3.js