d3 data array to summary object (e.g., "SELECT x, count(*) FROM y GROUP BY x")

gistfile1.js

// This may not be the most efficient way to do this, but it's pretty clean

var yourObject = d3.nest()
  .key(function(d) { return d; })
  .rollup(function(d) { return d.length; })
  .map(yourArray);

// e.g., 
// var input  = ["this","is","a","test","for","this","method"];
// var output = {"this":2,"is":1,"a":1,"test":1,"for":1,"method":1}