<meta charset="utf-8">

<style>

.links line {

  stroke: #999;

  stroke-opacity: 0.6;

}

.nodes circle {

  stroke: #fff;

  stroke-width: 1.5px;

}

</style>

<svg width="960" height="600"></svg>

<script src="https://d3js.org/d3.v4.min.js"></script>

<script>

//create somewhere to put the force directed graph

var svg = d3.select("svg"),

    width = +svg.attr("width"),

    height = +svg.attr("height");

var nodes_data =  [

    {"name": "Travis", "sex": "M"},

    {"name": "Rake", "sex": "M"},

    {"name": "Diana", "sex": "F"},

    {"name": "Rachel", "sex": "F"},

    {"name": "Shawn", "sex": "M"},

    {"name": "Emerald", "sex": "F"}

    ]

//set up the simulation 

//nodes only for now 

var simulation = d3.forceSimulation()

//add nodes

.nodes(nodes_data);

//add forces

//we're going to add a charge to each node 

//also going to add a centering force

simulation

    .force("charge_force", d3.forceManyBody())

    .force("center_force", d3.forceCenter(width / 2, height / 2));

//draw circles for the nodes 

var node = svg.append("g")

        .attr("class", "nodes")

        .selectAll("circle")

        .data(nodes_data)

        .enter()

        .append("circle")

        .attr("r", 5)

        .attr("fill", "red");  

//add tick instructions: 

simulation.on("tick", tickActions );

//Time for the links 

//Create links data 

var links_data = [

{"source": "Travis", "target": "Rake"},

    {"source": "Diana", "target": "Rake"},

    {"source": "Diana", "target": "Rachel"},

    {"source": "Rachel", "target": "Rake"},

    {"source": "Rachel", "target": "Shawn"},

    {"source": "Emerald", "target": "Rachel"}

]

//Create the link force 

//We need the id accessor to use named sources and targets 

var link_force =  d3.forceLink(links_data)

                        .id(function(d) { return d.name; })

//Add a links force to the simulation

//Specify links  in d3.forceLink argument   

simulation.force("links",link_force)

//draw lines for the links 

var link = svg.append("g")

      .attr("class", "links")

    .selectAll("line")

    .data(links_data)

    .enter().append("line")

      .attr("stroke-width", 2);        

function tickActions() {

    //update circle positions each tick of the simulation 

    node

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

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

    //update link positions 

    //simply tells one end of the line to follow one node around

    //and the other end of the line to follow the other node around

    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; });

  }                    

</script>