D3 Examples - Brushing Bar Chart

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<!DOCTYPE html>
<meta charset="utf-8">
<style>
​
svg {
  font: 10px sans-serif;
}
​
​
.bar {
  fill: steelblue;
  clip-path: url(#clip);
}
  
.subBar { 
  fill: gray;
  opacity: 0.5;
}
​
.axis path,
.axis line {
  fill: none;
  stroke: #000;
  shape-rendering: crispEdges;
}
​
.brush .extent {
  stroke: #fff;
  fill: steelblue;
  fill-opacity: .25;
  shape-rendering: crispEdges;
}
​
</style>
<body>
<script src="https://d3js.org/d3.v3.min.js"></script>
<script>
  
var data = [];
​
for (var i = 0; i < 300; i++) {
  var datum = {};
  datum.date = i;
  datum.price = Math.floor(Math.random() * 600);
  data.push(datum);
}  
  
var margin = {top: 10, right: 10, bottom: 100, left: 40},
    margin2 = {top: 430, right: 10, bottom: 20, left: 40},
    width = 750 - margin.left - margin.right,
    height = 500 - margin.top - margin.bottom,
    height2 = 500 - margin2.top - margin2.bottom;
​
var x = d3.scale.ordinal().rangeBands([0, width], .1),
    x2 = d3.scale.ordinal().rangeBands([0, width], .1),
    y = d3.scale.linear().range([height, 0]),
    y2 = d3.scale.linear().range([height2, 0]);
​
var xAxis = d3.svg.axis().scale(x).orient("bottom"),
    xAxis2 = d3.svg.axis().scale(x2).orient("bottom").tickValues([]),
    yAxis = d3.svg.axis().scale(y).orient("left");
​
        x.domain(data.map(function(d){ return d.date}));
      y.domain([0, d3.max(data, function(d) { return d.price;})]);
    x2.domain(x.domain());
      y2.domain(y.domain());
        
  var brush = d3.svg.brush()
                              .x(x2) 
                              .on("brush", brushed);
​
var svg = d3.select("body").append("svg")
    .attr("width", width + margin.left + margin.right)
    .attr("height", height + margin.top + margin.bottom);
​
var focus = svg.append("g")
    .attr("class", "focus")
    .attr("transform", "translate(" + margin.left + "," + margin.top + ")");
    
var context = svg.append("g")
    .attr("class", "context")
    .attr("transform", "translate(" + margin2.left + "," + margin2.top + ")");
​
  focus.append("g")
      .attr("class", "x axis")
      .attr("transform", "translate(0," + height + ")")
      .call(xAxis);
​
  focus.append("g")
      .attr("class", "y axis")
      .call(yAxis);
     
  console.log(x(data[0].date))
    enter(data)
  updateScale(data)
  
  var subBars = context.selectAll('.subBar')
                                    .data(data)
    
  subBars.enter().append("rect")
          .classed('subBar', true)
            .attr(
        {
        height: function (d)
        {
          return height2 - y2(d.price);
        },
        width: function(d){ return x.rangeBand()},
        x: function(d) {
​
          return x2(d.date);
        },
        y: function(d)
        {
          return y2(d.price)
        }
      })
​
  context.append("g")
      .attr("class", "x axis")
      .attr("transform", "translate(0," + height2 + ")")
      .call(xAxis2);
​
  context.append("g")
      .attr("class", "x brush")
      .call(brush)
    .selectAll("rect")
      .attr("y", -6)
      .attr("height", height2 + 7);
  
​
​
​
function brushed() {
    var selected = null; 
      selected =  x2.domain()
                .filter(function(d){
                        return (brush.extent()[0] <= x2(d)) && (x2(d) <= brush.extent()[1]);
                            });
  
    var start;
    var end;
        
    if(brush.extent()[0] != brush.extent()[1])
      {
        start = selected[0];
            end = selected[selected.length - 1] + 1;
      } else { 
                start = 0;
                end = data.length;
      }
​
    var updatedData = data.slice(start, end);
​
    update(updatedData);
    enter(updatedData);
    exit(updatedData);
    updateScale(updatedData)
 
​
}
 
  function updateScale(data)
  { 
            var tickScale = d3.scale.pow().range([data.length / 10, 0]).domain([data.length, 0]).exponent(.5)
​
    var brushValue = brush.extent()[1] - brush.extent()[0];
    if(brushValue === 0){
      brushValue = width;
    }
​
    var tickValueMultiplier = Math.ceil(Math.abs(tickScale(brushValue)));  
    var filteredTickValues = data.filter(function(d, i){return i % tickValueMultiplier === 0}).map(function(d){ return d.date})
​
    focus.select(".x.axis").call(xAxis.tickValues(filteredTickValues));
    focus.select(".y.axis").call(yAxis);
  }
  
  function update(data)
  {
          x.domain(data.map(function(d){ return d.date}));
          y.domain([0, d3.max(data, function(d) { return d.price;})]);
​
      var bars =  focus.selectAll('.bar')
          .data(data)
      bars
        .attr(
        {  
          height: function (d, i)
          { 
            return height - y(d.price);
          },
          width: function(d){ 
            return x.rangeBand()
          },
          x: function(d) {
​
            return x(d.date);
          },
          y: function(d)
          {
            return y(d.price)
          }
        })
​
  } 
  
  function exit(data)
  {
        var bars =  focus.selectAll('.bar').data(data)
        bars.exit().remove()
  }
  
  function enter(data)
  {
        x.domain(data.map(function(d){ return d.date}));
          y.domain([0, d3.max(data, function(d) { return d.price;})]);
​
      var bars =  focus.selectAll('.bar')
          .data(data)
      bars.enter().append("rect")
        .classed('bar', true)
        .attr(
        {  
          height: function (d, i)
          { 
            return height - y(d.price);
          },
          width: function(d){ 
            return x.rangeBand()
          },
          x: function(d) {
 
            return x(d.date);
          },
          y: function(d)
          {
            return y(d.price)
          }
        })
  }
​
</script>
​
    