Lots of examples of using d3.nest function
See it running at [/GerHobbelt/3695277] - original at [/phoebebright/3176159]
Documentation: [https://github.com/mbostock/d3/wiki/Arrays]
Modified http://d3js.org/d3.v2.js to a secure url
Modified http://gerhobbelt.github.com/bl.ocks.org-hack/fixit.js to a secure url
https://d3js.org/d3.v2.js
https://ajax.googleapis.com/ajax/libs/jquery/1.7.2/jquery.min.js
https://gerhobbelt.github.com/bl.ocks.org-hack/fixit.js