multi series line chart

<!DOCTYPE html>
<meta charset="utf-8">
<style>

body {
  font: 12px Helvetica;
}

.axis path,
.axis line {
  fill: none;
  stroke: #000;
  shape-rendering: crispEdges;
}

.x.axis line {
  display: none;
}

.network-line{
  fill: none;
  stroke: steelblue;
  stroke-width: 3px;
}

.network-line:hover{
  fill: none;
  stroke: red;
  stroke-width: 3px;
}

.network_name {
  font-weight: bold;
  opacity:1;
}

#tooltip {
  background: rgba(255, 255, 255, 0.95);
  position:absolute;
  height:auto;
  visibility:hidden;
  z-index:9999;
  padding:5px;
  border: 1px solid #ddd;
  padding: 5px 3px 0px 5px;
  font-family: arial, sans-serif;
  -webkit-box-shadow: 2px 2px 2px rgba(0, 0, 0, 0.3);
  -moz-box-shadow: 2px 2px 2px rgba(0, 0, 0, 0.3);
  box-shadow: 2px 2px 2px rgba(0, 0, 0, 0.3);
}

#main {
  line-height: .5em;
}

#viewers, #show, #show_rating {
  font-weight: bold !important;
}

#network, #year {
  font-weight: bold;
}

.y-text {
  font-weight: bold;
}

</style>
<body>

<div id="tooltip">
    <span id="network">hi</span>, <span id="year">year</span>
    <p id="main">Average audience: <span id="viewers"></span></p>
    <p id="main">Top show: <span id="show"></span> </p>
    <p id="main">Largest audience: <span id="show_rating"></span></p>
  </div>

var margin = {top: 20, right: 90, bottom: 30, left: 50},
    width = 700 - margin.left - margin.right,
    height = 400 - margin.top - margin.bottom;

var color = d3.scale.category10();

var x = d3.scale.linear()
    .range([0, width])
    .domain([2002,2013])

var y = d3.scale.linear()
    .range([height, 0]);

var xAxis = d3.svg.axis()
    .scale(x)
    .orient("bottom")
    .tickFormat(function(d) { return d});

var yAxis = d3.svg.axis()
    .scale(y)
    .tickSize(5)
    .ticks(8)
    .orient("left")
    .tickFormat(function(d) { return d + "m"});

var line = d3.svg.line()
    .x(function(d) { return x(d.year); })
    .y(function(d) { return y(d.val); })

var svg = d3.select("body").append("svg")
    .attr("width", width + margin.left + margin.right)
    .attr("height", height + margin.top + margin.bottom)
    .append("g")
    .attr("transform", "translate(" + margin.left + "," + margin.top + ")");

d3.csv("data3.csv", function(error, data) {
 color.domain(d3.keys(data[0]).filter(function(key) { return key !== "year"; }));

data.forEach(function(d) {
    d.year = +d.year;
    d.val = +d.val;
  });

viewersByNetwork = d3.nest()
      .key(function(d) { return d.network})
      .entries(data);

console.log(viewersByNetwork);

y.domain([0,d3.max(data.map(function(d) { return d.val; }))]);

svg.append("g")
      .attr("class", "x axis")
      .attr("transform", "translate(0," + height + ")")
      .call(xAxis);

svg.append("g")
      .attr("class", "y axis")
      .call(yAxis);

svg.append("g")
      .attr("class", "y axis")
      .call(yAxis)
      .append("text")
      .attr("class","y-text")
      .attr("transform", "rotate(-90)")
      .attr("y", -50)
      .attr("dy", ".71em")
      .style("text-anchor", "end")
      .text("Primetime viewers during the week of Sept.22-29");

var linesContainer = svg.append("g")

linesContainer.selectAll(".network-line")
      .data(viewersByNetwork)
      .enter()
      .append("path")
      .attr("class", "network-line")
      .attr("d", function(d) { return line(d.values); })
      .style("stroke", function(d) {return color(d.network); });

var labelElements = svg.append("g")
      .attr("class", "network_name")

var label = labelElements.selectAll(".g-label-element")
      .data(data.filter(function(d) { return d.year }))
      .enter().append("g")
      .attr("class", "g-label-element")
      .attr("transform", function(d) { return "translate(" + x(d.year) + "," + y(d.val) + ")"; } );

label.append("circle")
      .attr("class","circle")
      .attr("r", 3)
      .style("fill", function(d) {return color(d.network); })
      .on("mouseover", function(d){
              d3.select(this)
                .transition()
                .duration(100)
                .attr("r", 6)
                .style("stroke", "#000")
                .style("stroke-width",1)
              d3.select("#tooltip")
                .style("left", (d3.event.pageX) + 15 + "px")
                .style("top", (d3.event.pageY) - 5 + "px")
                .transition()
                .style("visibility", "visible");
              d3.select("#viewers")
                .text(d.val + "m" );
              d3.select("#show")
                .text( d.show);
              d3.select("#show_rating")
                .text( d.show_rating );
                d3.select("#network")
                .text( d.network );
                d3.select("#year")
                .text( d.year );
           })

.on("mouseout", function(d){
              d3.select(this)
                .transition()
                .attr("r", 3)
                .style("stroke", "none")
                .style("stroke-width", 0)
              d3.select("#tooltip")
                .transition()
                .style("visibility", "hidden");
           });

label.append("text")
      .attr("class","network_name")
      .attr("x", 10)
      .text(function(d) { if (d.network == "UPN" || d.network == "WB" || d.year !== 2013) {return ""} else {return d.network}; });

});

</script>

Modified http://d3js.org/d3.v3.min.js to a secure url

Modified http://d3js.org/colorbrewer.v1.min.js to a secure url

https://d3js.org/d3.v3.min.js

https://d3js.org/colorbrewer.v1.min.js