Line chart with zoom in d3.js

Notes:

Brush the chart to zoom. Double click to re-initialize.

Start by understanding how to build a basic line chart, and how brushing works in d3.js.

A class line is added to the line. It allows to select this class later on to update the line position.

It is possible to react to double click thanks to the on("dblclick",...) function.

<!DOCTYPE html>
<meta charset="utf-8">

<!-- Load d3.js -->
<script src="https://d3js.org/d3.v4.js"></script>

<!-- Create a div where the graph will take place -->
<div id="my_dataviz"></div>

<script>

// set the dimensions and margins of the graph
var margin = {top: 10, right: 30, bottom: 30, left: 60},
    width = 460 - margin.left - margin.right,
    height = 400 - margin.top - margin.bottom;

// append the svg object to the body of the page
var svg = d3.select("#my_dataviz")
  .append("svg")
    .attr("width", width + margin.left + margin.right)
    .attr("height", height + margin.top + margin.bottom)
  .append("g")
    .attr("transform",
          "translate(" + margin.left + "," + margin.top + ")");

//Read the data
d3.csv("https://raw.githubusercontent.com/holtzy/data_to_viz/master/Example_dataset/3_TwoNumOrdered_comma.csv",

  // When reading the csv, I must format variables:
  function(d){
    return { date : d3.timeParse("%Y-%m-%d")(d.date), value : d.value }
  },

  // Now I can use this dataset:
  function(data) {

    // Add X axis --> it is a date format
    var x = d3.scaleTime()
      .domain(d3.extent(data, function(d) { return d.date; }))
      .range([ 0, width ]);
    xAxis = svg.append("g")
      .attr("transform", "translate(0," + height + ")")
      .call(d3.axisBottom(x));

    // Add Y axis
    var y = d3.scaleLinear()
      .domain([0, d3.max(data, function(d) { return +d.value; })])
      .range([ height, 0 ]);
    yAxis = svg.append("g")
      .call(d3.axisLeft(y));

    // Add a clipPath: everything out of this area won't be drawn.
    var clip = svg.append("defs").append("svg:clipPath")
        .attr("id", "clip")
        .append("svg:rect")
        .attr("width", width )
        .attr("height", height )
        .attr("x", 0)
        .attr("y", 0);

    // Add brushing
    var brush = d3.brushX()                   // Add the brush feature using the d3.brush function
        .extent( [ [0,0], [width,height] ] )  // initialise the brush area: start at 0,0 and finishes at width,height: it means I select the whole graph area
        .on("end", updateChart)               // Each time the brush selection changes, trigger the 'updateChart' function

    // Create the line variable: where both the line and the brush take place
    var line = svg.append('g')
      .attr("clip-path", "url(#clip)")

    // Add the line
    line.append("path")
      .datum(data)
      .attr("class", "line")  // I add the class line to be able to modify this line later on.
      .attr("fill", "none")
      .attr("stroke", "steelblue")
      .attr("stroke-width", 1.5)
      .attr("d", d3.line()
        .x(function(d) { return x(d.date) })
        .y(function(d) { return y(d.value) })
        )

    // Add the brushing
    line
      .append("g")
        .attr("class", "brush")
        .call(brush);

    // A function that set idleTimeOut to null
    var idleTimeout
    function idled() { idleTimeout = null; }

    // A function that update the chart for given boundaries
    function updateChart() {

      // What are the selected boundaries?
      extent = d3.event.selection

      // If no selection, back to initial coordinate. Otherwise, update X axis domain
      if(!extent){
        if (!idleTimeout) return idleTimeout = setTimeout(idled, 350); // This allows to wait a little bit
        x.domain([ 4,8])
      }else{
        x.domain([ x.invert(extent[0]), x.invert(extent[1]) ])
        line.select(".brush").call(brush.move, null) // This remove the grey brush area as soon as the selection has been done
      }

      // Update axis and line position
      xAxis.transition().duration(1000).call(d3.axisBottom(x))
      line
          .select('.line')
          .transition()
          .duration(1000)
          .attr("d", d3.line()
            .x(function(d) { return x(d.date) })
            .y(function(d) { return y(d.value) })
          )
    }

    // If user double click, reinitialize the chart
    svg.on("dblclick",function(){
      x.domain(d3.extent(data, function(d) { return d.date; }))
      xAxis.transition().call(d3.axisBottom(x))
      line
        .select('.line')
        .transition()
        .attr("d", d3.line()
          .x(function(d) { return x(d.date) })
          .y(function(d) { return y(d.value) })
      )
    });

})

</script>

Notes:

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