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Ds in action: advanced data visualization techniques and examples

Linda Hamilton

Dec 30, 2024 am 07:11 AM

Ds in action: advanced data visualization techniques and examples

Basics

First, we need an HTML file to import the D3.js library and prepare a canvas to place our chart.

<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Getting Started with D3.js Example</title>
  <script src="https://d3js.org/d3.v7.min.js"></script>
</head>
<body>
  <svg width="500" height="500"></svg>
</body>
</html>

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Create a simple line graph

// Assume we have the following data
var data = [4, 8, 15, 16, 23, 42];
 
// Create an SVG canvas
var svg = d3.select("svg"),
    margin = {top: 20, right: 20, bottom: 30, left: 50},
    width = +svg.attr("width") - margin.left - margin.right,
    height = +svg.attr("height") - margin.top - margin.bottom;
 
// Create x and y scales
var x = d3.scaleLinear()
    .domain(d3.extent(data, d => d))
    .range([0, width]);
 
var y = d3.scaleLinear()
    .domain([0, d3.max(data)])
    .range([height, 0]);
 
// Create the x and y axes
var xAxis = d3.axisBottom(x),
    yAxis = d3.axisLeft(y);
 
// Add axis
svg.append("g")
    .attr("transform", "translate(0," + height + ")")
    .call(xAxis);
 
svg.append("g")
    .call(yAxis);
 
// Draw the polyline
var line = d3.line()
    .x(d => x(d))
    .y(d => y(d));
 
svg.append("path")
    .datum(data)
    .attr("class", "line")
    .attr("d", line);

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Creating a Bar Chart

// Suppose we have the following data
var data = [4, 8, 15, 16, 23, 42];
 
// Creating the SVG canvas and scale
var svg = d3.select("svg").attr("width", 500).attr("height", 500);
var margin = {top: 20, right: 20, bottom: 30, left: 40};
var width = +svg.attr("width") - margin.left - margin.right;
var height = +svg.attr("height") - margin.top - margin.bottom;
var x = d3.scaleBand().rangeRound([0, width]).padding(0.1);
var y = d3.scaleLinear().rangeRound([height, 0]);
 
// Mapping data to scale
x.domain(data.map(function(d) { return d; }));
y.domain([0, d3.max(data)]);
 
// Creating an SVG g Element
var g = svg.append("g")
    .attr("transform", "translate(" + margin.left + "," + margin.top + ")");
 
// Adding x and y axes
g.append("g")
    .attr("transform", "translate(0," + height + ")")
    .call(d3.axisBottom(x));
 
g.append("g")
    .call(d3.axisLeft(y));
 
// Draw a bar chart
g.selectAll(".bar")
    .data(data)
    .enter().append("rect")
    .attr("class", "bar")
    .attr("x", function(d) { return x(d); })
    .attr("y", function(d) { return y(d); })
    .attr("width", x.bandwidth())
    .attr("height", function(d) { return height - y(d); });

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Create a pie chart

// Suppose we have the following data
var data = [4, 8, 15, 16, 23, 42];
 
// Creating the SVG canvas and scale
var svg = d3.select("svg").attr("width", 500).attr("height", 500);
var radius = Math.min(svg.attr("width"), svg.attr("height")) / 2;
 
// Creating an arc scale
var arc = d3.arc().outerRadius(radius).innerRadius(0);
var pie = d3.pie().value(function(d) { return d; });
 
// Draw a pie chart
var g = svg.append("g")
    .attr("transform", "translate(" + radius + "," + radius + ")");
 
var arcs = g.selectAll("arc")
    .data(pie(data))
    .enter().append("g")
    .attr("class", "arc");
 
arcs.append("path")
    .attr("d", arc)
    .attr("fill", function(d, i) { return d3.schemeCategory10[i]; });
 
arcs.append("text")
    .attr("transform", function(d) { return "translate(" + arc.centroid(d) + ")"; })
    .attr("dy", ".35em")
    .text(function(d) { return d.data; });

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Interactivity and animation

Interactivity example: adding hover effects to a bar chart

// Assuming that the bar chart base code already exists
// ...
 
// Add hover effects
g.selectAll(".bar")
    .on("mouseover", function(event, d) {
        d3.select(this)
            .transition()
            .duration(200)
            .attr("fill", "orange"); // Mouseover color change
 
        // Show Data Tips
        var tooltip = g.append("text")
            .attr("class", "tooltip")
            .attr("x", x(d) + x.bandwidth() / 2)
            .attr("y", y(d) - 10)
            .text(d);
    })
    .on("mouseout", function(event, d) {
        d3.select(this)
            .transition()
            .duration(200)
            .attr("fill", "steelblue"); // Restore original color
 
        // Remove data tips
        g.selectAll(".tooltip").remove();
    });

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Animation example: Smooth transition line chart data update

// Assume that there is already a line chart basic code
// ...
 
// Update data
var newData = [8, 15, 16, 23, 42, 45];
 
// Update scale domain
x.domain(d3.extent(newData));
y.domain([0, d3.max(newData)]);
 
// Update axis
g.select(".axis--x").transition().duration(750).call(xAxis);
g.select(".axis--y").transition().duration(750).call(yAxis);
 
// Update path
var path = g.select(".line");
path.datum(newData).transition().duration(750).attr("d", line);

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Complex graphs: force-directed graphs

Force-directed graphs show the relationship between nodes and edges, which is very suitable for visualizing data such as networks and social graphs.

// Assume we have data on nodes and edges
var nodes = [{id: "A"}, {id: "B"}, {id: "C"}];
var links = [{source: nodes[0], target: nodes[1]}, {source: nodes[1], target: nodes[2]}];
 
// Creating the SVG Canvas
var svg = d3.select("svg"),
    width = +svg.attr("width"),
    height = +svg.attr("height");
 
// Creating a Force Simulation
var simulation = d3.forceSimulation(nodes)
    .force("link", d3.forceLink(links).id(function(d) { return d.id; }))
    .force("charge", d3.forceManyBody())
    .force("center", d3.forceCenter(width / 2, height / 2));
 
// Creating links and nodes
var link = svg.append("g")
    .attr("stroke", "#999")
    .attr("stroke-opacity", 0.6)
  .selectAll("line")
  .data(links)
  .join("line")
    .attr("stroke-width", 2);
 
var node = svg.append("g")
    .attr("stroke", "#fff")
    .attr("stroke-width", 1.5)
  .selectAll("circle")
  .data(nodes)
  .join("circle")
    .attr("r", 5)
    .call(d3.drag()
        .on("start", dragstarted)
        .on("drag", dragged)
        .on("end", dragended));
 
node.append("title")
    .text(function(d) { return d.id; });
 
simulation.on("tick", ticked);
 
function ticked() {
  link
      .attr("x1", function(d) { return d.source.x; })
      .attr("y1", function(d) { return d.source.y; })
      .attr("x2", function(d) { return d.target.x; })
      .attr("y2", function(d) { return d.target.y; });
 
  node
      .attr("cx", function(d) { return d.x; })
      .attr("cy", function(d) { return d.y; });
}
 
// Drag event handling function
function dragstarted(event, d) {
  if (!event.active) simulation.alphaTarget(0.3).restart();
  d.fx = d.x;
  d.fy = d.y;
}
 
function dragged(event, d) {
  d.fx = event.x;
  d.fy = event.y;
}
 
function dragended(event, d) {
  if (!event.active) simulation.alphaTarget(0);
  d.fx = null;
  d.fy = null;
}

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Map Visualization

D3.js can work with geographic data formats such as GeoJSON to create interactive maps. This includes countries, states, city boundaries, etc.

Basic steps:

Load map data: Use D3's d3.json or d3.geoJson to load GeoJSON data.
Create scale: Define a geographic projection and scale, such as Mercator or Albers USA.
Bind data and draw: Bind GeoJSON data to SVG path elements and apply a projection.
Add interactions: Such as hover effects, click events, etc.

d3.json("world.geojson").then(function(geoData) {
  var svg = d3.select("svg"),
      projection = d3.geoMercator().scale(130).translate([400, 250]),
      path = d3.geoPath().projection(projection);
 
  svg.selectAll("path")
    .data(geoData.features)
    .enter().append("path")
    .attr("d", path)
    .attr("fill", "#ccc")
    .attr("stroke", "#fff");
});

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Data binding and dynamic update

Basic steps:

Initialize data binding: Use the data() method to bind data to DOM elements.
Enter, Update, Exit mode: process new data, update existing data, and remove useless data.
Dynamic update: monitor data changes, re-execute binding and rendering processes.

var svg = d3.select("svg"),
    data = [4, 8, 15, 16, 23, 42];
 
// Initialize the bar chart
var bars = svg.selectAll("rect").data(data);
 
bars.enter().append("rect")
    .attr("x", function(d, i) { return i * 50; })
    .attr("y", function(d) { return 300 - d; })
    .attr("width", 40)
    .attr("height", function(d) { return d; });
 
// Dynamic Updates
setInterval(function() {
  data = data.map(function(d) { return Math.max(0, Math.random() * 50); });
 
  bars.data(data)
    .transition()
    .duration(500)
    .attr("y", function(d) { return 300 - d; })
    .attr("height", function(d) { return d; });
}, 2000);

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Complex charts and advanced techniques

Advanced techniques:

Use D3 component libraries: Libraries like D3fc provide advanced chart components to simplify the creation of complex charts.
Animation and transition: Use the transition() method to create smooth animation effects.
Interactivity: Add click and hover events, and use brush and zoom functions to enhance user experience.
Performance optimization: Use selectAll(), data(), enter(), exit() reasonably to reduce DOM operations, and use requestAnimationFrame() to optimize animation performance.

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