score:4

Accepted answer

The problem appears to be the last statement in your force-on-tick callback:

node.attr("x", function(d) { return d.x; })
    .attr("y", function(d) { return d.y; });

SVG paths have no such x/y attributes. Try translating the path instead:

node.attr('transform', function(d) { return 'translate(' + d.x + ',' + d.y + ')'; });

score:2

The code as above wasn't working, the snippet below displays both pie charts, in the right location, with edges visible and with pie chart colors:

<!DOCTYPE html>
<html lang="en">
<head>
    <script type="text/javascript" src="http://d3js.org/d3.v3.min.js"></script>

    <style>

        .node {
            stroke: #fff;
            stroke-width: 1.5px;
        }

        .link {
            stroke: #808080;
            stroke-opacity: .6;
        }

    </style>
</head>
<body>

<script type="text/javascript">

    graph = { "nodes":[
                    {"proportions": [{"group": 1, "value": 1},
                                     {"group": 2, "value": 2},
                                     {"group": 3, "value": 3}]},
                    {"proportions": [{"group": 1, "value": 2},
                                     {"group": 2, "value": 2},
                                     {"group": 3, "value": 2}]}],
              "links":[{"source": 0, "target": 1, "length": 500, "width": 1}]
    }

    var width = 960,
    height = 500,
    radius = 25,
    color = d3.scale.category10();

    var pie = d3.layout.pie()
        .sort(null)
        .value(function(d) { return d.value; });

    var arc = d3.svg.arc()
        .outerRadius(radius)
        .innerRadius(0);

    var svg = d3.select("body").append("svg")
        .attr("width", width)
        .attr("height", height);

    var force = d3.layout.force()
        .charge(-120)
        .linkDistance(4 * radius)
        .size([width, height]);

    force.nodes(graph.nodes)
         .links(graph.links)
         .start();

    var link = svg.selectAll(".link")
        .data(graph.links)
        .enter().append("line")
        .attr("class", "link");

    var node = svg.selectAll(".node")
        .data(graph.nodes)
        .enter().append("g")
        .attr("class", "node");

    node.selectAll("path")
        .data(function(d, i) {return pie(d.proportions); })
        .enter()
        .append("svg:path")
        .attr("d", arc)
        .attr("fill", function(d, i) { return color(d.data.group); });;

    force.on("tick", function() {
        link.attr("x1", function(d) { return d.source.x; })
        .attr("y1", function(d) { return d.source.y; })
        .attr("x2", function(d) { return d.target.x; })
        .attr("y2", function(d) { return d.target.y; });

        node.attr("x", function(d) { return d.x; })
            .attr("y", function(d) { return d.y; })
            .attr("transform", function(d) { return "translate(" + d.x + "," + d.y + ")"});
    });
</script>
</body>
</html>

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