D3 Examples - Date slider - filtering data

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<!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: 9px;
    }
​
    .track,
    .track-inset,
    .track-overlay {
      stroke-linecap: round;
    }
​
    .track {
      stroke: #000;
      stroke-opacity: 0.3;
      stroke-width: 10px;
    }
​
    .track-inset {
      stroke: #dcdcdc;
      stroke-width: 8px;
    }
​
    .track-overlay {
      pointer-events: stroke;
      stroke-width: 30px;
      stroke: transparent;
      cursor: crosshair;
    }
​
    .handle {
      fill: #fff;
      stroke: #000;
      stroke-opacity: 0.5;
      stroke-width: 1.25px;
    }
  </style>
</head>
​
<body>
<div id="slider"></div>
<div id="vis"></div>
​
  <script>
var dataset;
​
var formatDateIntoYear = d3.timeFormat("%b %Y");
var formatDate = d3.timeFormat("%b %d ");
var parseDate = d3.timeParse("%m/%d/%y");
​
var startDate = new Date("2014-11-01"),
    endDate = new Date("2017-04-01");
​
var margin = {top:0, right:50, bottom:0, left:50},
    width = 560 - margin.left - margin.right,
    height = 80 - margin.top - margin.bottom;
​
////////// slider //////////
​
var svgSlider = d3.select("#slider")
    .append("svg")
    .attr("width", width + margin.left + margin.right )
    .attr("height", height);
    
var x = d3.scaleTime()
    .domain([startDate, endDate])
    .range([0, width])
    .clamp(true);
​
var slider = svgSlider.append("g")
    .attr("class", "slider")
    .attr("transform", "translate(" + margin.left + "," + height / 2 +")");
​
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() { update(x.invert(d3.event.x))
                        
}))
​
slider.insert("g", ".track-overlay")
    .attr("class", "ticks")
    .attr("transform", "translate(0," + 12 + ")")
  .selectAll("text")
    .data(x.ticks(5))
    .enter()
    .append("text")
    .attr("x", x)
    .attr("y", 10)
    .attr("text-anchor", "middle")
    .text(function(d) { return formatDateIntoYear(d); });
​
var handle = slider.insert("rect", ".track-overlaybox")
    .attr("class", "handle")
    .attr("x", 0)
    .attr("y", -40)
    .attr("height", 80) 
    .attr("width", 1)
        .style("stroke", "red")
        .style("opacity", "0.5")
​
var handlebox = slider.insert("rect", ".track-overlay")
    .attr("class", "handle")
    .attr("x", -27)
    .attr("y", -40)
    .attr("height", 70) 
    .attr("width", 50)
        .style("stroke", "blue")
        .style("opacity", "0.3")
​
var label = slider.append("text")  
    .attr("class", "label")
    .attr("text-anchor", "middle")
    .text(formatDate(startDate))
    .attr("transform", "translate(-3," + (-22) + ")")
​
////////// plot //////////
​
var svgPlot = d3.select("#vis")
    .append("svg")
    .attr("width", width + margin.left + margin.right)
    .attr("height", height);
​
var plot = svgPlot.append("g")
    .attr("class", "plot")
    .attr("transform", "translate(" + margin.left + "," + margin.top + ")");
    
​
d3.csv("circles.csv", prepare, function(data) {
  dataset = data;
  drawPlot(dataset);
})
​
function prepare(d) {
  d.id = d.id;
  d.date = parseDate(d.date);
  return d;
}
​
function drawPlot(data) {
  var locations = plot.selectAll(".location")
    .data(data);
​
  // 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", height/2)
    .style("fill", function(d) { return d3.hsl(d.date/1000000000, 0.8, 0.8)})
    .style("stroke", function(d) { return d3.hsl(d.date/1000000000, 0.7, 0.7)})
    .style("opacity", 0.5)
    .attr("r", 8)
      .transition()
      .duration(400)
      .attr("r", 25)
        .transition()
        .attr("r", 8);
​
  // if filtered dataset has less circles than already existing, remove excess
  locations.exit()
    .remove();
}
​
function update(h) {
  // update position and text of label according to slider scale
  handle.attr("x", x(h));
  handlebox.attr("x", x(h)-28);
  label
    .attr("x", x(h))
    .text(formatDate(h));
​
  // filter data set and redraw plot
  var newData = dataset.filter(function(d) {
    return d.date < h;
  })
  drawPlot(newData);
}
</script>
</body>
    