Создание легенды для пузырьковой диаграммы с помощью D3

Я пытался изучить D3 (в частности, Bubble Charts). Я создал очень простую диаграмму здесь:

//This is making the demensions for the circles and canvas
    //The format and color is for hovering over the circles for the dialog box
    var diameter = 1500,
        format = d3.format(",d"),
        color = d3.scale.category20c();

    //This makes the canvas that the bubble chart will be made on
    var canvas = d3.select("body").append("svg")
                                  .attr("width", diameter)
                                  .attr("height", diameter)
                                  .append("g")
                                    .attr("transform", "translate(50,50)");

    //This is the size of the actual bubbles in the chart
    var pack = d3.layout.pack()
            .size([900, 900])
            .padding(85);

    //This is adding the data into the bubbles and creating their size
    d3.json("CountryData.js", function (data) {
        var nodes = pack.nodes(data);

        var node = canvas.selectAll(".node")
                    .data(nodes)
                    .enter()
                    .append("g")
                        .attr("class", "node")
                        .attr("transform", function (d) { return "translate(" + d.x + "," + d.y + ")"; });

        //This is the actual bubbles
        node.append("circle")
            .attr("r", function (d) {return d.r;})
            .style("fill", function (d, i) { return color(i); });


        //This is the text inside the bubbles
        node.append("text")
            .text(function (d) { return d.children ? "" : d.name; })
            .style("text-anchor", "middle")

        //This is the dialog box
        node.append("title")
            .text(function (d) { return d.name + ": " + format(d.value) + "" + "medals"; });


    });

Я пытался добавить легенду, которая покажет «Азию», «Северную Америку», «Ближний Восток» и т. д. и их цвета. Самое близкое, что у меня было, это показывать поля с цветами и отображать названия цветов. Я пытался использовать это: Легенда в круговой диаграмме D3 в качестве справки . Я могу приложить, как я пытался сделать легенду, но мне кажется, что это будет слишком много кода для поста. Вот мои данные:

{
"name" : "Region Olympic Medals",
"value" : 10000,
"children" : [
    {
        "name" : "Asia",
        "value" : 451,
        "children" : [
            {"name" : "Summer Gold", "value" : 114},
            {"name" : "Summer Silver", "value" : 172},
            {"name" : "Summer Bronze", "value" : 158},
            {"name" : "Winter Gold", "value" : 1},
            {"name" : "Winter Silver", "value" : 1},
            {"name" : "Winter Bronze", "value" : 2}
        ]
    },
    {
        "name" : "Australia & Oceaina",
        "value" : 26,
        "children" : [
            {"name" : "Summer Gold", "value" : 4},
            {"name" : "Summer Silver", "value" : 7},
            {"name" : "Summer Bronze", "value" : 15},
            {"name" : "Winter Gold", "value" : 0},
            {"name" : "Winter Silver", "value" : 0},
            {"name" : "Winter Bronze", "value" : 0}
        ]
    },
    {
        "name" : "Caribbean",
        "value" : 1136,
        "children" : [
            {"name" : "Summer Gold", "value" : 306},
            {"name" : "Summer Silver", "value" : 319},
            {"name" : "Summer Bronze", "value" : 381},
            {"name" : "Winter Gold", "value" : 42},
            {"name" : "Winter Silver", "value" : 41},
            {"name" : "Winter Bronze", "value" : 47}
        ]
    },
    {

            "name" : "Central America",
            "value" : 26,
            "children" : [
                {"name" : "Summer Gold", "value" : 4},
                {"name" : "Summer Silver", "value" : 3},
                {"name" : "Summer Bronze", "value" : 4},
                {"name" : "Winter Gold", "value" : 0},
                {"name" : "Winter Silver", "value" : 0},
                {"name" : "Winter Bronze", "value" : 0}
        ]
    },
    {

        "name" : "Europe",
        "value" : 7264,
        "children" : [
            {"name" : "Summer Gold", "value" : 1924},
            {"name" : "Summer Silver", "value" : 1993},
            {"name" : "Summer Bronze", "value" : 2257},
            {"name" : "Winter Gold", "value" : 362},
            {"name" : "Winter Silver", "value" : 366},
            {"name" : "Winter Bronze", "value" : 362}
        ]
    },
    {

        "name" : "Middle East",
        "value" : 2696,
        "children" : [
            {"name" : "Summer Gold", "value" : 280},
            {"name" : "Summer Silver", "value" : 331},
            {"name" : "Summer Bronze", "value" : 361},
            {"name" : "Winter Gold", "value" : 535},
            {"name" : "Winter Silver", "value" : 582},
            {"name" : "Winter Bronze", "value" : 607}
        ]
    },
    {

        "name" : "North America",
        "value" : 7,
        "children" : [
            {"name" : "Summer Gold", "value" : 4},
            {"name" : "Summer Silver", "value" : 1},
            {"name" : "Summer Bronze", "value" : 2},
            {"name" : "Winter Gold", "value" : 0},
            {"name" : "Winter Silver", "value" : 0},
            {"name" : "Winter Bronze", "value" : 0}
        ]
    },
    {

        "name" : "South America",
        "value" : 6273,
        "children" : [
            {"name" : "Summer Gold", "value" : 1220},
            {"name" : "Summer Silver", "value" : 1014},
            {"name" : "Summer Bronze", "value" : 335},
            {"name" : "Winter Gold", "value" : 1421},
            {"name" : "Winter Silver", "value" : 1193},
            {"name" : "Winter Bronze", "value" : 1090}
        ]
    },
    {

        "name" : "Sub-Saharan Africa",
        "value" : 1847,
        "children" : [
            {"name" : "Summer Gold", "value" : 485},
            {"name" : "Summer Silver", "value" : 549},
            {"name" : "Summer Bronze", "value" : 628},
            {"name" : "Winter Gold", "value" : 50},
            {"name" : "Winter Silver", "value" : 59},
            {"name" : "Winter Bronze", "value" : 76}
        ]
    }
]

}