gistfile1.js

function groupData(data, nGroups) {
    var out = [];
    data.sort(function(a, b) { return a > b; })
    var hop = data[data.length-1] / nGroups;
    for(var i=0; i<data.length; i++) {
        var index = Math.ceil(data[i] / hop);
        if(!out[index]) out[index] = [];
        out[index].push(data[i]);
    }
    return out;
}

console.log(groupData([1,2,3,4,5,100, 40,600,6000], 10));
console.log(groupData([1,2,3,4,5], 5));