hierarchy.js

function build_hierarchy(list, key, tuple_func) {
    var direct_hierarchy = list
        .map(tuple_func)
        .reduce(function(obj, tuple) {
            tuple[0] in obj ? obj[tuple[0]].push(tuple[1]) : obj[tuple[0]] = [tuple[1]];
            return obj;
        }, {});

    var hierarchy = Object.keys(direct_hierarchy)
        .reduce(function(obj, type) {
            var entity = { Name: type };
            entity[key] = obj.input[type];

            obj.result.push(entity);

            return obj;
        }, {result: [], input: direct_hierarchy}).result;

    return hierarchy;

}

var hierarchy = {"ProductHierarchy":{}};

hierarchy["ProductHierarchy"]["Suppliers"] = build_hierarchy(data.ProductCollection, "Categories", function(a) {
    return [a.SupplierName, a];
}).map(function(a) {
    a["Categories"] = build_hierarchy(a.Categories, "Products", function(a) {
        return [a.Category, a];
    });

    return a;
});