Date slider - histogram legend

Date slider using a histogram as colour legend. Slider adapted from Mike Bostock's drag slider.

Related examples:

<!DOCTYPE html>
<head>
  <meta charset="utf-8">
  <script src="https://d3js.org/d3.v4.min.js"></script>
  <style>
    body {
      font-family:"avenir next", Arial, sans-serif;
      font-size: 12px;
      color: #696969;
    }

.ticks {
      font-size: 10px;
    }

.track,
    .track-inset,
    .track-overlay {
      stroke-linecap: round;
    }

.track {
      stroke: #dcdcdc;
      stroke-width: 10px;
    }

.track-inset {
      stroke: #dcdcdc;
      stroke-width: 8px;
    }

.track-overlay {
      pointer-events: stroke;
      stroke-width: 50px;
      stroke: transparent;
      cursor: crosshair;
    }

.handle {
      fill: #fff;
      stroke: #000;
      stroke-opacity: 0.5;
      stroke-width: 1.25px;
    }
  </style>
</head>

var histHeight = height/5;

var parseDate = d3.timeParse("%d-%b-%y");
var formatDateIntoYear = d3.timeFormat("%Y");

var startDate = new Date("2004-11-01"),
    endDate = new Date("2017-04-01");

var dateArray = d3.timeYears(startDate, d3.timeYear.offset(endDate, 1));

var colours = d3.scaleOrdinal()
    .domain(dateArray)
    .range(['#ffc388','#ffb269','#ffa15e','#fd8f5b','#f97d5a','#f26c58','#e95b56','#e04b51','#d53a4b','#c92c42','#bb1d36','#ac0f29','#9c0418','#8b0000']);

// x scale for time
var x = d3.scaleTime()
    .domain([startDate, endDate])
    .range([0, width])
    .clamp(true);

// y scale for histogram
var y = d3.scaleLinear()
    .range([histHeight, 0]);

////////// histogram set up //////////

// set parameters for histogram
var histogram = d3.histogram()
    .value(function(d) { return d.date; })
    .domain(x.domain())
    .thresholds(x.ticks(d3.timeYear));

var svg = d3.select("#vis")
    .append("svg")
    .attr("width", width + margin.left + margin.right)
    .attr("height", height + margin.top + margin.bottom);

var hist = svg.append("g")
    .attr("class", "histogram")
    .attr("transform", "translate(" + margin.left + "," + margin.top + ")");

////////// plot set up //////////

var dataset;

var plot = svg.append("g")
    .attr("class", "plot")
    .attr("transform", "translate(" + margin.left + "," + margin.top + ")");

////////// load data //////////

d3.csv("histogram.csv", prepare, function(data) {
  
  // group data for bars
  var bins = histogram(data);

// y domain based on binned data
  y.domain([0, d3.max(bins, function(d) { return d.length; })]);

bar.append("text")
      .attr("dy", ".75em")
      .attr("y", "6")
      .attr("x", function(d) { return (x(d.x1) - x(d.x0))/2; })
      .attr("text-anchor", "middle")
      .text(function(d) { if (d.length>15) { return d.length; } })
      .style("fill", "white");

dataset = data;
  drawPlot(dataset);
})

////////// slider //////////

var currentValue = 0;

var slider = svg.append("g")
    .attr("class", "slider")
    .attr("transform", "translate(" + margin.left + "," + (margin.top+histHeight+5) + ")");

slider.append("line")
    .attr("class", "track")
    .attr("x1", x.range()[0])
    .attr("x2", x.range()[1])
  .select(function() { return this.parentNode.appendChild(this.cloneNode(true)); })
    .attr("class", "track-inset")
  .select(function() { return this.parentNode.appendChild(this.cloneNode(true)); })
    .attr("class", "track-overlay")
    .call(d3.drag()
        .on("start.interrupt", function() { slider.interrupt(); })
        .on("start drag", function() {
          currentValue = d3.event.x;
          update(x.invert(currentValue)); 
        })
    );

slider.insert("g", ".track-overlay")
    .attr("class", "ticks")
    .attr("transform", "translate(0," + 18 + ")")
  .selectAll("text")
    .data(x.ticks(10))
    .enter()
    .append("text")
    .attr("x", x)
    .attr("y", 10)
    .attr("text-anchor", "middle")
    .text(function(d) { return formatDateIntoYear(d); });

var handle = slider.insert("circle", ".track-overlay")
    .attr("class", "handle")
    .attr("r", 9);

function drawPlot(data) {
  var locations = plot.selectAll(".location")
    .data(data, function(d) { return d.id; });

// if filtered dataset has more circles than already existing, transition new ones in
  locations.enter()
    .append("circle")
    .attr("class", "location")
    .attr("cx", function(d) { return x(d.date); })
    .attr("cy", function(d) { return Math.random()*((height/2+50)-(height/2-50))+(height/2-50); })
    .style("fill", function(d) { return colours(d3.timeYear(d.date)); })
    .style("stroke", function(d) { return colours(d3.timeYear(d.date)); })
    .style("opacity", 0.3)
    .attr("r", 5)
      .transition()
      .duration(400)
      .attr("r", 15)
        .transition()
        .attr("r", 5);

// if filtered dataset has less circles than already existing, remove excess
  locations.exit()
    .remove();
}

function update(h) {
  handle.attr("cx", x(h));

// filter data set and redraw plot
  var newData = dataset.filter(function(d) {
    return d.date < h;
  })
  drawPlot(newData);

// histogram bar colours
  d3.selectAll(".bar")
    .attr("fill", function(d) {
      if (d.x0 < h) {
        return colours(d.x0);
      } else {
        return "#eaeaea";
      }
    })
}

function prepare(d) {
  d.date = parseDate(d.date);
  d.value = +d.value;
  return d;
}
  
</script>
</body>

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