Area chart with line and individual data points.




This post follows the previous basic area chart. It shows how to display the trend line on top, with the individual observations represented as circle as well. It is actually a mix between a scatterplot, a line chart and an area chart.


Area chart section

Steps:

  • Start by understanding how to build a basic area chart.

  • Adding the line: a first approach could be to add stroke to the area. But this highlights the whole border, not only the top.. The workaround is to plot a line chart on top using the d3.line() function.

  • Adding the dots: this is done appending circles like for a classic scatterplot. Note: do it only if the number of data point is not to high.
<!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: 50},
    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) {

    // Keep only the 90 first rows
    data = data.filter(function(d,i){ return i<90})

    // Add X axis --> it is a date format
    var x = d3.scaleTime()
      .domain(d3.extent(data, function(d) { return d.date; }))
      .range([ 0, width ]);
    svg.append("g")
      .attr("transform", "translate(0," + (height+5) + ")")
      .call(d3.axisBottom(x).ticks(5).tickSizeOuter(0));

    // Add Y axis
    var y = d3.scaleLinear()
      .domain( d3.extent(data, function(d) { return +d.value; }) )
      .range([ height, 0 ]);
    svg.append("g")
      .attr("transform", "translate(-5,0)")
      .call(d3.axisLeft(y).tickSizeOuter(0));

    // Add the area
    svg.append("path")
      .datum(data)
      .attr("fill", "#69b3a2")
      .attr("fill-opacity", .3)
      .attr("stroke", "none")
      .attr("d", d3.area()
        .x(function(d) { return x(d.date) })
        .y0( height )
        .y1(function(d) { return y(d.value) })
        )

    // Add the line
    svg.append("path")
      .datum(data)
      .attr("fill", "none")
      .attr("stroke", "#69b3a2")
      .attr("stroke-width", 4)
      .attr("d", d3.line()
        .x(function(d) { return x(d.date) })
        .y(function(d) { return y(d.value) })
        )

    // Add the line
    svg.selectAll("myCircles")
      .data(data)
      .enter()
      .append("circle")
        .attr("fill", "red")
        .attr("stroke", "none")
        .attr("cx", function(d) { return x(d.date) })
        .attr("cy", function(d) { return y(d.value) })
        .attr("r", 3)

})

</script>

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