【D3.js】Focus + Context 折线图

利用D3.js库实现Focus+Context的折线图。读取data.tsv文件数据
index.html
<!DOCTYPE html>
<meta charset="utf-8">
<style>

svg {
  font: 10px sans-serif;
}

.axis path,
.axis line {
  fill: none;
  stroke: #000;
  shape-rendering: crispEdges;
}

.line {
  fill: none;
  clip-path: url(#clip);                            //将多余的超出坐标系范围的线段裁剪掉
  stroke: steelblue;
  stroke- 1.5px;
}

.brush .extent {
  stroke: #fff;
  fill-opacity: .125;
  shape-rendering: crispEdges;
}

</style>
<body>
<script src="https://cdnjs.cloudflare.com/ajax/libs/d3/3.5.5/d3.min.js"></script>
<script>

var margin = {top: 10, right: 10, bottom: 100, left: 40},
    margin2 = {top: 430, right: 10, bottom: 20, left: 40},
    width = 960 - margin.left - margin.right,
    height = 500 - margin.top - margin.bottom,
    height2 = 500 - margin2.top - margin2.bottom;
    
var color = d3.scale.category10();

var parseDate = d3.time.format("%Y%m%d").parse;

var x = d3.time.scale().range([0, width]),
    x2 = d3.time.scale().range([0, width]),
    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"),
    yAxis = d3.svg.axis().scale(y).orient("left");
    
var line = d3.svg.line()
    .interpolate("basis")
    .x(function(d) { return x(d.date); })
    .y(function(d) { return y(d.temperature);});
    
var line2 = d3.svg.line()
    .interpolate("basis")
    .x(function(d) { return x2(d.date); })
    .y(function(d) { return y2(d.temperature); }); 

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);

svg.append("defs").append("clipPath")
    .attr("id", "clip")
  .append("rect")
    .attr("width", width)
    .attr("height", height);

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 + ")");

d3.tsv("data.tsv",  function(error, data) {

  color.domain(d3.keys(data[0]).filter(function(key) { return key !== "date"; }));

  data.forEach(function(d) {
    d.date = parseDate(d.date);
  });

  var cities = color.domain().map(function(name) {
    return {
      name: name,
      values: data.map(function(d) {
        return {date: d.date, temperature: +d[name]};
      })
    };
  });

  x.domain(d3.extent(data, function(d) { return d.date; }));

  y.domain([
    d3.min(cities, function(c) { return d3.min(c.values, function(v) { return v.temperature; }); }),
    d3.max(cities, function(c) { return d3.max(c.values, function(v) { return v.temperature; }); })
  ]);

  x2.domain(x.domain());
  y2.domain(y.domain());
  
  
 var city = focus.selectAll(".city")
	   .data(cities)
	 .enter().append("g")
	   .attr("class", "city");

  city.append("path")
      .attr("class", "line")
      .attr("d", function(d) { return line(d.values); })
      .style("stroke", function(d) { return color(d.name); });

  focus.append("g")
      .attr("class", "x axis")
      .attr("transform", "translate(0," + height + ")")
      .call(xAxis);

  focus.append("g")
      .attr("class", "y axis")
      .call(yAxis);
      
      
  var city2 = context.selectAll(".city")
	   .data(cities)
	 .enter().append("g")
	   .attr("class", "city");

	  city2.append("path")
	      .attr("class", "line")
	      .attr("d", function(d) { return line2(d.values); })
	      .style("stroke", function(d) { return color(d.name); });

  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() {
  x.domain(brush.empty() ? x2.domain() : brush.extent());
  focus.selectAll(".line").attr("d", function(d) { return line(d.values); });
  focus.select(".x.axis").call(xAxis);
}

</script>
效果图例如以下：