Multi y-axis with mouseover

This is a simple extension to d3noob's block, but adding a third y-axis to the frame. Additionally when mousing over a line, the line is highlighted, and the other lines are partially dimmed.

This is a multiple line graph demonstrating the display of seperate colour coded y axes for each line. This was written using d3.js v4 and is a follow on to the multiple line graph example here.

This graph is part of the code samples for the update to the book D3 Tips and Tricks to version 4 of d3.js.

forked from d3noob's block: Dual axes in v4

forked from lwthatcher's block: Three y-axes in v4

<!DOCTYPE html>
<meta charset="utf-8">
<style> /* set the CSS */

.line {
  fill: none;
  stroke: steelblue;
  stroke-width: 2px;
}
  
.line--fade {
  opacity: 0.5;  
}
  
.line--hover {
  stroke-width: 3px;
  opacity: 1.0;
}

.axisSteelBlue text{
  fill: steelblue;
}

.axisRed text{
  fill: red;
}
  
.axisPurple text {
  fill: purple;
}

</style>
<body>

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

// set the dimensions and margins of the graph
var margin = {top: 20, right: 40, bottom: 30, left: 50},
    width = 960 - margin.left - margin.right,
    height = 500 - margin.top - margin.bottom;

// parse the date / time
var parseTime = d3.timeParse("%d-%b-%y");

// set the ranges
var x = d3.scaleTime().range([0, width]);
var y0 = d3.scaleLinear().range([height, 0]);
var y1 = d3.scaleLinear().range([height, 0]);
var y2 = d3.scaleLinear().range([height, 0]);

// define the 1st line
var valueline = d3.line()
    .x(function(d) { return x(d.date); })
    .y(function(d) { return y0(d.close); });

// define the 2nd line
var valueline2 = d3.line()
    .x(function(d) { return x(d.date); })
    .y(function(d) { return y1(d.open); });
  
var valueline3 = d3.line()
    .x(function(d) { return x(d.date); })
    .y(function(d) { return y2(Math.log(d.open)); });

// append the svg obgect to the body of the page
// appends a 'group' element to 'svg'
// moves the 'group' element to the top left margin
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 + ")");

// Get the data
d3.csv("data4.csv", function(error, data) {
  if (error) throw error;

// format the data
  data.forEach(function(d) {
      d.date = parseTime(d.date);
      d.close = +d.close;
      d.open = +d.open;
  });

// Scale the range of the data
  x.domain(d3.extent(data, function(d) { return d.date; }));
  y0.domain([0, d3.max(data, function(d) {return Math.max(d.close);})]);
  y1.domain([0, d3.max(data, function(d) {return Math.max(d.open); })]);
  y2.domain([0, d3.max(data, function(d) {return Math.max(Math.log(d.open)); })]);
  
  // Add the valueline path.
  svg.append("path")
      .data([data])
      .attr("class", "line l1")
      .attr("d", valueline)
  		.on("mouseover", mouseover)
  		.on("mouseout", mouseout);

// Add the valueline2 path.
  svg.append("path")
      .data([data])
      .attr("class", "line l2")
      .style("stroke", "red")
      .attr("d", valueline2)
      .on("mouseover", mouseover)
  		.on("mouseout", mouseout);
  
  // Add the valueline3 path.
  svg.append("path")
      .data([data])
      .attr("class", "line")
      .style("stroke", "purple")
      .attr("d", valueline3)
  		.on("mouseover", mouseover)
  		.on("mouseout", mouseout);

// Add the X Axis
  svg.append("g")
      .attr("transform", "translate(0," + height + ")")
      .call(d3.axisBottom(x));

// Add the Y0 Axis
  svg.append("g")
      .attr("class", "axisSteelBlue")
      .call(d3.axisLeft(y0));

// Add the Y1 Axis
  svg.append("g")
      .attr("class", "axisRed")
      .attr("transform", "translate( " + width + ", 0 )")
      .call(d3.axisRight(y1));

// Add the Y2 Axis
  svg.append("g")
      .attr("class", "axisPurple")
      .attr("transform", "translate( " + width + ", 0 )")
      .call(d3.axisLeft(y2));
  
  function mouseover(d) {
    var me = this;
    //d3.select(d.line).classed("line--hover", true);
    d3.selectAll(".line").classed("line--hover", function() {
      return (this === me);
    }).classed("line--fade", function() {
      return (this !== me);
    });
  }
  
  function mouseout(d) {
    d3.selectAll(".line")
      .classed("line--hover", false)
      .classed("line--fade", false);
  }
  
});

</script>
</body>

https://d3js.org/d3.v4.min.js