d3.js V3 力定向图和未链接的节点

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

var color = d3.scaleOrdinal(d3.schemeCategory20);

var simulation = d3.forceSimulation()
    .force("link", d3.forceLink().id(function(d) { return d.id; }))
    .force("charge", d3.forceManyBody())
    .force("center", d3.forceCenter(width / 2, height / 2));

var states = [
     {id:"Georgia",abbreviation:"GA"},
     {id:"Hawaii",abbreviation:"HI"},
     {id:"Idaho",abbreviation:"ID"},
     {id:"Montana",abbreviation:"MT"},
     {id:"Nevada",abbreviation:"NV"},
     {id:"North Carolina",abbreviation:"NC"},
     {id:"Oregon",abbreviation:"OR"},
     {id:"South Carolina",abbreviation:"SC"},
     {id:"Tennessee",abbreviation:"TN"},
]

var data = [
     ['Georgia','North Carolina'],
     ['Georgia','South Carolina'],
     ['Georgia','Tennessee'],
     ['Hawaii'],
     ['Idaho',  'Montana'],
     ['Idaho',  'Nevada'],
     ['Idaho',  'Oregon']
]


var links = data.filter(link => link[0] && link[1])
            .map(link => ({source: link[0], target: link[1]}))
  

  var link = svg.append("g")
      .attr("class", "links")
    .selectAll("line")
    .data(links)
    .enter().append("line")
      .attr("stroke-width", 1);

  var node = svg.append("g")
      .attr("class", "nodes")
    .selectAll("circle")
    .data(states)
    .enter().append("circle")
      .attr("r", 5)
    .call(d3.drag()
          .on("start", dragstarted)
          .on("drag", dragged)
          .on("end", dragended));

  node.append("title")
      .text(function(d) { return d.abbreviation; });

  simulation
      .nodes(states)
      .on("tick", ticked);

  simulation.force("link")
      .links(links);

  function ticked() {
    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("cx", function(d) { return d.x; })
        .attr("cy", function(d) { return d.y; });
  }

function dragstarted(d) {
  if (!d3.event.active) simulation.alphaTarget(0.3).restart();
  d.fx = d.x;
  d.fy = d.y;
}

function dragged(d) {
  d.fx = d3.event.x;
  d.fy = d3.event.y;
}

function dragended(d) {
  if (!d3.event.active) simulation.alphaTarget(0);
  d.fx = null;
  d.fy = null;
}

.links line {
  stroke: #999;
  stroke-opacity: 0.6;
}

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

<script src="https://d3js.org/d3.v4.min.js"></script>
<svg width="500" height="200"></svg>