A connected scatter plot with tooltip
(and more)




This post describes how to build a connected scatter plot with d3.js. The chart includes tooltip, and curve smoothing. Learn more about the theory of connected scatter plot in data-to-viz.com.


Connected scatter section

Steps:

  • See the previous example for a basic connected scatterplot.

  • Note that the transformation for segments to smooth curve is a breeze thanks to the .curve() function. See this post that is dedicated to it.

  • Adding tooltip uses the usual technique. It is extensively described here.
<!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>

<!-- Circle are black when hovered-->
<style>
.myCircle:hover {
  stroke: black;
}
</style>


<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/D3-graph-gallery/master/DATA/connectedscatter.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 ]);
    svg.append("g")
      .attr("transform", "translate(0," + height + ")")
      .call(d3.axisBottom(x));

    // Add Y axis
    var y = d3.scaleLinear()
      .domain( [8000, 9200])
      .range([ height, 0 ]);
    svg.append("g")
      .call(d3.axisLeft(y));

    // Add the line
    svg.append("path")
      .datum(data)
      .attr("fill", "none")
      .attr("stroke", "black")
      .attr("stroke-width", 1.5)
      .attr("d", d3.line()
        .curve(d3.curveBasis) // Just add that to have a curve instead of segments
        .x(function(d) { return x(d.date) })
        .y(function(d) { return y(d.value) })
        )

    // create a tooltip
    var Tooltip = d3.select("#my_dataviz")
      .append("div")
      .style("opacity", 0)
      .attr("class", "tooltip")
      .style("background-color", "white")
      .style("border", "solid")
      .style("border-width", "2px")
      .style("border-radius", "5px")
      .style("padding", "5px")

      // Three function that change the tooltip when user hover / move / leave a cell
      var mouseover = function(d) {
        Tooltip
          .style("opacity", 1)
      }
      var mousemove = function(d) {
        Tooltip
          .html("Exact value: " + d.value)
          .style("left", (d3.mouse(this)[0]+70) + "px")
          .style("top", (d3.mouse(this)[1]) + "px")
      }
      var mouseleave = function(d) {
        Tooltip
          .style("opacity", 0)
      }

    // Add the points
    svg
      .append("g")
      .selectAll("dot")
      .data(data)
      .enter()
      .append("circle")
        .attr("class", "myCircle")
        .attr("cx", function(d) { return x(d.date) } )
        .attr("cy", function(d) { return y(d.value) } )
        .attr("r", 8)
        .attr("stroke", "#69b3a2")
        .attr("stroke-width", 3)
        .attr("fill", "white")
        .on("mouseover", mouseover)
        .on("mousemove", mousemove)
        .on("mouseleave", mouseleave)
})


</script>

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