D3 Examples - Spurious Correlations Dual Axis Line Chart

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<!DOCTYPE html>
<meta charset="utf-8">
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<script src="https://d3js.org/d3.v4.min.js"></script>
​
<style type="text/css">
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:root {
    --highlight-color:red;
}
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.axis .tick {
  stroke-width:0.5px;
  stroke-opacity: .5;
}
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.axis path {
  stroke: none;
}
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.line {
  stroke: black;
  fill: none;
  stroke-width: 1.5;
}
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.axis.cheese text {
  fill: var(--highlight-color);
}
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.cheese-circle {
  fill: var(--highlight-color);
}
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.line.cheese {
  stroke: var(--highlight-color);
}
​
</style>
​
<body>
<p class="details"></p>
</body>
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<script>
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var margin = {top: 20, right: 40, bottom: 30, left: 40};
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var width = 900 - margin.left - margin.right,
    height = 250 - margin.top - margin.bottom;
​
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 + ")");
​
var xScale = d3.scaleLinear()
  .domain([1999, 2010])
  .range([0, width]);
​
var cheeseScale = d3.scaleLinear()
  .domain([9, 12])
  .range([height, 0]);
​
var doctorateScale = d3.scaleLinear()
  .domain([400, 1000])
  .range([height, 0])
​
var xAxis = d3.axisBottom(xScale)
  .tickFormat(d3.format("d"));
​
var cheeseAxis = d3.axisLeft(cheeseScale)
  .ticks(4)
  .tickSize(-width);
​
var doctorateAxis = d3.axisRight(doctorateScale)
  .ticks(4)
  .tickSize(0);
​
d3.csv("cheese_engineers.csv", ready)
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function ready(error, data) {
​
  if (error) return console.warn(error);
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  svg.append('g')
    .attr('class', 'x axis')
    .attr('transform', 'translate(0, ' + height + ')')
    .call(xAxis)
​
  svg.append('g')
    .attr('class', 'cheese axis')
    .call(cheeseAxis)
​
    svg.append('g')
    .attr('class', 'doctorate axis')
    .attr('transform', 'translate(' + width + ', 0)')
    .call(doctorateAxis)
​
  function select_year(d) {
    var this_year = 'year' + d.year;
    d3.select(".details").text('In ' + d.year + ', ' + d.cheese + ' pounds of mozzarella cheese was consumed, and ' + d.doctorates + ' Civil Engineering Doctorates were awarded')
    d3.selectAll('.circle')
      .attr('r', 5)
    d3.selectAll('.' + this_year)
      .transition()
      .attr('r', 15)
  }
​
  function deselect_year(d) {
    d3.selectAll('.circle')
      .transition()
      .attr('r', 5)
  }
​
  var cheeseCircle = svg.selectAll('.cheese-circle')
    .data(data)
   .enter().append('circle')
     .attr('class', 'cheese-circle')
     .attr("class", function(d) { return 'cheese-circle circle ' + 'year' + d.year })
     .attr('r', 5)
     .attr('cx', function(d) { return xScale(d.year) })
     .attr('cy', function(d) { return cheeseScale(d.cheese)})
     .attr('fill', 'red')
     .on('mouseover', function(d) {
        select_year(d)
      })
      .on('mouseout', function(d) {
        deselect_year(d)
      });
​
  var cheeseLineGenerator = d3.line()
    .x(function(d) { return xScale(d.year) })
    .y(function(d) { return cheeseScale(d.cheese)})
​
  var cheesePath = svg.append('path')
    .datum(data)
    .attr('class', 'line')
    .attr('d', cheeseLineGenerator(data))
    .style('stroke', 'red')
​
  var doctorateCircle = svg.selectAll('.doctorate-circle')
    .data(data)
    .enter().append('circle')
    .attr("class", function(d) { return 'doctorate-circle circle ' + 'year' + d.year })     .attr('r', 5)
    .attr('cx', function(d) { return xScale(d.year) })
    .attr('cy', function(d) { return doctorateScale(d.doctorates)})
    .on('mouseover', function(d) {
      select_year(d)
    })
    .on('mouseout', function(d) {
      deselect_year(d)
    });
​
   var doctorateLineGenerator = d3.line()
    .x(function(d) { return xScale(d.year) })
    .y(function(d) { return doctorateScale(d.doctorates)}) 
​
  var doctoratePath = svg.append('path')
    .datum(data)
    .attr('class', 'line')
    .attr('d', doctorateLineGenerator(data));
​
  svg.append("text")
    .attr("transform", "rotate(-90)")
    .attr("y", 0 - margin.left)
    .attr("x",0 - (height / 2))
    .attr("dy", "1em")
    .style("text-anchor", "middle")
    .text("Mozzarella cheese consumption (lbs)")
    .attr('fill', 'red');    
​
  svg.append("text")
    .attr("transform", "rotate(-90)")
    .attr("y", width + 20)
    .attr("x",0 - (height / 2))
    .attr("dy", "1em")
    .style("text-anchor", "middle")
    .text("Civil Engineering Doctorates");   
}
​
</script>
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