D3 Examples - sync candlebar and line, 2-y-axis

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<!DOCTYPE html>
<meta charset="utf-8">
<style>
​
.axis--x path {
  display: none;
}
​
.line {
  fill: none;
  stroke: steelblue;
  stroke-width: 1.5px;
}
​
</style>
​
<svg width="960" height="500"></svg>
​
<script src="//d3js.org/d3.v4.min.js"></script>
<script> 
​
var svg = d3.select("svg");  
  
var  
    margin = {top: 20, right: 80, bottom: 30, left: 50},
    width = svg.attr("width") - margin.left - margin.right,
    height = svg.attr("height") - margin.top - margin.bottom;
  
var  
    g = svg.append("g")
                .attr("transform", "translate(" + margin.left + "," + margin.top + ")");
​
// ---------- step 1 above: create svg and g  --------------------------
  
  
var parseTime = d3.timeParse("%Y%m%d");
​
var x = d3.scaleTime().rangeRound([0, width]),
// var x = d3.scaleBand().rangeRound([0, width]).padding(0.2),
​
    y = d3.scaleLinear().range([height, 0]);
  
    y_return = d3.scaleLinear().range([height, 0]);
​
var line = d3.line()
                            .curve(d3.curveBasis)
                .x(function(d) { return x(d.Date); })
                .y(function(d) {  return y_return(d.return); }); 
​
// ------------ step 3.a above: define scale functions with their ranges ----------
  
  
  
  
function type(d, _, columns) {
  
  d.Date = parseTime(+d.Date);
​
  for (var i = 1, n = columns.length, c; i < n; ++i) d[c = columns[i]] = +d[c];
  return d;  
} 
    
  
d3.csv("data_filled.csv", type,  function(error, data) {
  if (error) throw error;  
  
//   console.log(data.columns);
//   console.log(data); 
//   console.log(data[0].Date);  
  
​
​
// ---------------- step 2 above: get row-data and column-data ready -------------
  
  
        x.domain(d3.extent(data, function(d){return d.Date;}));
//   x.domain(data.map(function(d){return d.Date}));
// console.log(x.domain());  
   
  
  
    y_return.domain(d3.extent(data, function(d){return d.return;}));
// console.log(y_return.domain());
  
  y.domain(
    [d3.min(data.map(function(d){return d.Low;})), 
    d3.max(data.map(function(d){return d.High;}))] 
  );
//   console.log(y.domain());  
​
  
​
​
  
// ------------------ step 3.b above: set scale-func domain ----------------------
  
  
  g.append("g")
      .attr("class", "axis axis--x")
      .attr("transform", "translate(0," + height + ")")
      .call(d3.axisBottom(x));
​
var rightAxis = g.append("g")
      .attr("class", "axis axis--y")
        .attr("transform", "translate("+width+","+0+")")
      .call(d3.axisRight(y_return))
​
// legend ROR and pink
    rightAxis
        .append("text")
        .attr("x",-10)
      .attr("y", 6)
      .attr("dy", "0.71em")
        .attr("text-anchor", "end")
      .attr("fill", "#000")
      .text("ROR");
  
  rightAxis
        .append("rect")
        .attr("x", -30)
        .attr("y", 20)
        .attr("width", 15)
        .attr("height", 5)
        .attr("fill", "steelblue")
  
var leftAxis = g.append("g")
      .attr("class", "axis axis--y")
      .call(d3.axisLeft(y))
​
// legend price
leftAxis
    .append("text")
            .attr("x",10)
      .attr("y", 6)
      .attr("dy", "0.71em")
        .attr("text-anchor", "start")
      .attr("fill", "#000")
      .text("Price");
​
//   legend red
leftAxis
    .append("rect")
            .attr("x",10)
      .attr("y", 26)
      .attr("width", 15)
        .attr("height", 5)
      .attr("fill", "red")
leftAxis
        .append("text")
            .attr("x", 30)
            .attr("y", 36)
            .attr("dy", "-0.45em")
            .attr("stroke", "red")
            .attr("text-anchor", "start")
      .text("up");
  
//  legend green 
leftAxis
    .append("rect")
            .attr("x",10)
      .attr("y", 36)
      .attr("width", 15)
        .attr("height", 5)
      .attr("fill", "green")
leftAxis
        .append("text")
            .attr("x", 30)
            .attr("y", 46)
            .attr("dy", "-0.45em")
            .attr("stroke", "green")
            .attr("text-anchor", "start")
      .text("down");  
  
  
  var barWidth = width/data.length; 
//   console.log(barWidth);
  
  var candlebar = g.selectAll(".bar")
    .data(data)
    .enter().append("g")
      .attr("class", ".bar")
        .attr("transform", function(d, i) { return "translate(" + i * barWidth + ",0)"; });
  ;
​
    candlebar.append("line")
                  .attr("x1", barWidth/2)
                    .attr("x2", barWidth/2)
                    .attr("y1", function(d){ return y(d.High);})
                    .attr("y2", function(d){ return y(d.Low);})
                    .attr("stroke-width", 0.01)
                    .attr("stroke", "gray");
  
  
  candlebar.append("rect")
            .attr("y", function(d) { 
                                            if (d.Open > d.Close) {
                          return y(d.Open)
                        } else {
                            return y(d.Close);   
                        }}) 
  
            .attr("height", function(d) { 
                                            if (d.Open > d.Close) {
                          return (height - y(d.Open)) - (height - y(d.Close));
                        } else {
                          if (d.Open < d.Close) {
                          return (height - y(d.Close)) - (height - y(d.Open));
                        }}})
                          
                    .attr("fill", function(d){
                                            if (d.Open > d.Close) {
                          return "green" ;
                        } else {
                          if (d.Open < d.Close) {
                          return "red" ;
                        }}})
                        .attr("opacity", 0.2)
            .attr("width", barWidth);
  
  
//   return column data 
  var col_return = data.map(function(d){
    return {
​
        Date: d.Date,
        return: d.return
    
  }})
  
//   console.log(col_return);  
  
  var c =  g.append("path")
        .datum(col_return)
      .attr("class", "line")
      .attr("d", function(d) { return line(d);})
      .style("stroke", "steelblue");
  
// console.log(c);
  
// ---------- step 4 above: draw x-y-axis, lines, ... -----------------------------
  
});
​
​
</script>
 
    