Multiple Line Climate Plot with Zoom

This serves as an example of how to add a zoomable feature to a plot using a "brush". By selecting a window width in the bottom graph, the top graph is redrawn with that window extent. For this data this may not be all that interesting, but in principle it is an interesting technique.

<!DOCTYPE html>
<meta charset="utf-8">
<style>
 
svg {
  font: 10px sans-serif;
}
 
 
.axis path,
.axis line {
  fill: none;
  stroke: #000;
  shape-rendering: crispEdges;
}

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

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

.line {
  fill: none;
}

</style>
<body>
<script src="https://d3js.org/d3.v3.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").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 brush = d3.svg.brush()
    .x(x2)
    .on("brush", brush);
 
var line = d3.svg.line()
    .defined(function(d) { return !isNaN(d.temperature); })
    .interpolate("cubic")
    .x(function(d) { return x(d.date); })
    .y(function(d) { return y(d.temperature); });
 
var line2 = d3.svg.line()
    .defined(function(d) { return !isNaN(d.temperature); })
    .interpolate("cubic")
    .x(function(d) {return x2(d.date); })
    .y(function(d) {return y2(d.temperature); });
 
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("transform", "translate(" + margin.left + "," + margin.top + ")");
      
var context = svg.append("g")
  .attr("transform", "translate(" + margin2.left + "," + margin2.top + ")");
 
d3.csv("climate4.csv", 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 sources = 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(sources, function(c) { return d3.min(c.values, function(v) { return v.temperature; }); }),
              d3.max(sources, function(c) { return d3.max(c.values, function(v) { return v.temperature; }); }) ]);
    x2.domain(x.domain());
    y2.domain(y.domain());
    
    var focuslineGroups = focus.selectAll("g")
        .data(sources)
      .enter().append("g");
      
    var focuslines = focuslineGroups.append("path")
        .attr("class","line")
        .attr("d", function(d) { return line(d.values); })
        .style("stroke", function(d) {return color(d.name);})
        .attr("clip-path", "url(#clip)");
    
    focus.append("g")
        .attr("class", "x axis")
        .attr("transform", "translate(0," + height + ")")
        .call(xAxis);
 
    focus.append("g")
        .attr("class", "y axis")
        .call(yAxis);
        
    var contextlineGroups = context.selectAll("g")
        .data(sources)
      .enter().append("g");
    
    var contextLines = contextlineGroups.append("path")
        .attr("class", "line")
        .attr("d", function(d) { return line2(d.values); })
        .style("stroke", function(d) {return color(d.name);})
        .attr("clip-path", "url(#clip)");
 
    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 brush() {
  x.domain(brush.empty() ? x2.domain() : brush.extent());
  focus.selectAll("path.line").attr("d",  function(d) {return line(d.values)});
  focus.select(".x.axis").call(xAxis);
  focus.select(".y.axis").call(yAxis);
}
 
</script>

Modified http://d3js.org/d3.v3.min.js to a secure url

https://d3js.org/d3.v3.min.js