d3.pie() is a layout: it turns values into objects with startAngle, endAngle, value, index and data (sorted by value unless you call sort(null)). d3.arc() draws one as a wedge; an innerRadius makes a donut, padAngle and cornerRadius separate and round wedges, and arc.centroid(d) places labels:
<script src="https://cdn.jsdelivr.net/npm/d3@7.9.0/dist/d3.min.js"></script>
<script src="booknest-sales.js"></script>
<svg width="620" height="148" font-family="Arial" font-size="13"></svg>
<script>
const slices = d3.pie().sort(null)(SALES.ratings[0].counts); // 1 to 5 stars, in order
const arcs = [d3.arc().innerRadius(0).outerRadius(70),
d3.arc().innerRadius(38).outerRadius(70).padAngle(0.03).cornerRadius(4)];
arcs.forEach((arc, i) => {
const g = d3.select('svg').append('g')
.attr('transform', `translate(${150 + i * 300}, 74)`);
g.selectAll('path').data(slices).join('path').attr('d', arc)
.attr('fill', d => d3.schemeYlOrBr[5][d.index]);
g.selectAll('text').data(slices.filter(d => d.value > 20)).join('text')
.attr('transform', d => `translate(${arc.centroid(d)})`).attr('text-anchor', 'middle')
.text(d => `${d.index + 1}\u2605`);
});
</script>
Angles are radians clockwise from 12 o'clock: the five-star wedge (293 of 412 reviews) runs from 1.81 to 2π. For many small slices, a sorted bar chart (Ratings Bar Chart) reads far better than a pie.
<!doctype html>
<style>
body { margin: 0; padding: 8px; background: #fafaf7; font: 12px system-ui, sans-serif; color: #263238; }
svg { width: 100%; max-width: 600px; display: block; }
</style>
<script src="https://cdn.jsdelivr.net/npm/d3@7.9.0/dist/d3.min.js"></script>
<p>Book: <select id="book"></select> <span id="out"></span></p>
<svg viewBox="0 0 600 160" font-size="13"></svg>
<script>
// BookNest sample data, invented for these examples (not real sales)
const SALES = (() => {
const books = [
{ id: 1, key: 'harbor', title: 'The Quiet Harbor', author: 'Elena Marsh', genre: 'Fiction', color: '#1f5f8b', price: 18.99, rating: 4.6 },
{ id: 2, key: 'deepweb', title: 'Patterns of the Deep Web', author: 'Ravi Menon', genre: 'Technology', color: '#5b3f99', price: 39.5, rating: 4.3 },
{ id: 3, key: 'saffron', title: 'Salt and Saffron', author: 'Leila Haddad', genre: 'Cooking', color: '#e09a10', price: 24, rating: 4.8 },
{ id: 4, key: 'summit', title: 'Small Steps to Big Summits', author: 'Tom Okafor', genre: 'Self-Help', color: '#3f7d3a', price: 14.99, rating: 4.1 },
{ id: 5, key: 'clock', title: "The Clockmaker's Paradox", author: 'Iris Vale', genre: 'Science Fiction', color: '#b5452f', price: 16.2, rating: 4.5 },
{ id: 6, key: 'glass', title: 'Gardens in Glass', author: 'June Park', genre: 'Gardening', color: '#2a9d8f', price: 22.5, rating: 4.4 },
];
const units = { // units sold per month, January 2025 to August 2026
1: [40, 47, 46, 47, 57, 51, 46, 54, 60, 60, 71, 111, 52, 42, 49, 56, 59, 48, 53, 51],
2: [40, 37, 35, 41, 48, 43, 40, 42, 50, 53, 53, 84, 42, 35, 38, 41, 45, 41, 46, 46],
3: [46, 45, 41, 46, 53, 49, 46, 45, 60, 51, 63, 100, 48, 48, 49, 48, 53, 49, 48, 52],
4: [100, 80, 72, 70, 66, 66], // released March 2026
5: [48, 47, 54, 52, 65, 55, 57, 58, 64, 66, 75, 124, 58, 49, 59, 56, 63, 57, 54, 57],
6: [31, 30, 28, 35, 31, 32, 29, 30, 41, 36, 45, 64, 31, 30, 30, 38, 40, 38, 36, 38],
};
const months = d3.utcMonths(new Date('2025-01-01'), new Date('2026-09-01')).map(d3.utcFormat('%Y-%m'));
const sales = books.flatMap(b => units[b.id].map((n, i) =>
({ month: months[i + months.length - units[b.id].length], book: b.id, units: n })));
const ratings = [[4, 8, 20, 87, 293], [6, 10, 22, 95, 147], [2, 3, 8, 45, 342], [2, 3, 8, 24, 28],
[4, 8, 20, 90, 228], [4, 7, 20, 82, 147]].map((counts, i) => ({ book: i + 1, counts })); // 1 to 5 stars
const regions = [{ id: '826', name: 'United Kingdom', units: 1480 }, { id: '276', name: 'Germany', units: 1120 },
{ id: '250', name: 'France', units: 760 }, { id: '372', name: 'Ireland', units: 540 },
{ id: '528', name: 'Netherlands', units: 410 }, { id: '724', name: 'Spain', units: 320 }];
const links = [[5, 1, 38], [1, 3, 24], [2, 5, 18], [3, 6, 21], [4, 1, 12], [2, 6, 9], [4, 3, 15], [5, 6, 14]]
.map(([source, target, value]) => ({ source, target, value })); // customers who bought both
return { books, sales, ratings, regions, links };
})();
const select = d3.select('#book');
select.selectAll('option').data(SALES.books).join('option').attr('value', (d, i) => i).text(d => d.title);
const arcs = [d3.arc().innerRadius(0).outerRadius(72),
d3.arc().innerRadius(40).outerRadius(72).padAngle(0.03).cornerRadius(4)];
const groups = arcs.map((arc, i) => d3.select('svg').append('g')
.attr('transform', `translate(${150 + i * 300}, 80)`));
function draw(index) {
// pie() is a layout: values in, objects with startAngle, endAngle, value and index out
const slices = d3.pie().sort(null)(SALES.ratings[index].counts); // 1 to 5 stars, in order
arcs.forEach((arc, i) => {
groups[i].selectAll('path').data(slices).join('path').attr('d', arc)
.attr('fill', d => d3.schemeYlOrBr[5][d.index]).attr('stroke', '#fff');
groups[i].selectAll('text').data(slices.filter(d => d.endAngle - d.startAngle > 0.35)).join('text')
.attr('transform', d => `translate(${arc.centroid(d)})`).attr('text-anchor', 'middle')
.attr('dy', '0.35em').text(d => `${d.index + 1}★`);
});
const five = slices[4];
d3.select('#out').text(`five-star wedge: ${five.value} of ${d3.sum(slices, d => d.value)} reviews, ` +
`angles ${five.startAngle.toFixed(2)} to ${five.endAngle.toFixed(2)} rad`);
}
select.on('change', () => draw(+select.property('value')));
draw(0);
</script>