JSFiddle - React, Tailwind, and code Playground

HTML

<script src="https://cdnjs.cloudflare.com/ajax/libs/d3/3.5.17/d3.js"></script>
<div id="table">

</div>

JavaScript

var data = {
        "result" : [
                {
                        "_id" : {
                                "month" : 5,
                                "day" : 6,
                                "year" : 2014,
                                "env" : "A"
                        },
                        "ruleScore" : 83.25,
                        "jsPerPage" : 12,
                        "cssPerPage" : 4,
                        "imagesPerPage" : 7.75
                },
                {
                        "_id" : {
                                "month" : 5,
                                "day" : 6,
                                "year" : 2014,
                                "env" : "B"
                        },
                        "ruleScore" : 83,
                        "jsPerPage" : 12,
                        "cssPerPage" : 4,
                        "imagesPerPage" : 10
                },
                {
                        "_id" : {
                                "month" : 5,
                                "day" : 6,
                                "year" : 2014,
                                "env" : "C"
                        },
                        "ruleScore" : 83,
                        "jsPerPage" : 12,
                        "cssPerPage" : 5,
                        "imagesPerPage" : 10,
                },
                {
                        "_id" : {
                                "month" : 5,
                                "day" : 6,
                                "year" : 2014,
                                "env" : "D"
                        },
                        "ruleScore" : 83.08333333333333,
                        "jsPerPage" : 12,
                        "cssPerPage" : 6,
                        "imagesPerPage" : 9.25
                }
        ],
        "ok" : 1
};


var nested = d3.nest()
    .key(function(d) { return d._id.env; })
    .entries(data.result);

console.log(nested); ...