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>
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);
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); });
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; });
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();
});
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);
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;
}
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");
});
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);
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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