d3.hierarchy(data) gives each node data, depth, height (0 at a leaf), parent and children; sum(fn) stores in every value the total of its leaves, which size-based layouts read. A nested Map from d3.group works directly, so this file builds the catalog hierarchy for every figure in this section:
const SHELF = { Fiction: 'Novels', 'Science Fiction': 'Novels' }; // the rest: Nonfiction
function catalogTree(data, value = b => b.revenue) {
const nest = d3.group(data.books, b => SHELF[b.genre] ?? 'Nonfiction', b => b.genre);
return d3.hierarchy(nest) // a Map becomes the entry [undefined, map]
.sum(d => d.id ? value(d) : 0) // only books (the leaves) carry a value
.sort((a, b) => b.height - a.height || b.value - a.value);
}
const nodeName = n => n.depth === 0 ? 'BookNest' : n.children ? n.data[0] : n.data.title;The result has 15 nodes and 14 links: the root ($118,552 of revenue), the shelves Nonfiction ($81,372) and Novels ($37,180), six genres and six books. descendants(), leaves() and links() return what layouts draw. For tables with id and parent columns, d3.stratify() builds the same nodes; stratify().path() accepts paths such as Nonfiction/Cooking/Salt and Saffron.
<!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>Sum by <label><input type="radio" name="v" value="revenue" checked> revenue</label>
<label><input type="radio" name="v" value="units"> units</label></p>
<svg viewBox="0 0 600 330" font-size="12"></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 };
})();
// prepareSales(raw): parsed dates, sales linked to book objects, revenue and totals
function prepareSales(raw) {
const parse = d3.utcParse('%Y-%m'), books = raw.books.map(b => ({ ...b }));
const byId = d3.index(books, b => b.id);
const sales = raw.sales.map(s => ({ date: parse(s.month), book: byId.get(s.book),
units: s.units, revenue: s.units * byId.get(s.book).price }));
for (const [book, rows] of d3.group(sales, s => s.book)) {
book.units = d3.sum(rows, s => s.units);
book.revenue = d3.sum(rows, s => s.revenue);
}
const months = d3.rollups(sales, v => ({ units: d3.sum(v, s => s.units),
revenue: d3.sum(v, s => s.revenue) }), s => +s.date).map(([t, v]) => ({ date: new Date(t), ...v }))
.sort((a, b) => a.date - b.date);
const ratings = raw.ratings.map(r => ({ ...r, book: byId.get(r.book) }));
return { ...raw, books, sales, months, ratings };
}
// catalogTree(data, value): shelf → genre → book, as a d3.hierarchy summed by value
const SHELF = { Fiction: 'Novels', 'Science Fiction': 'Novels' }; // the rest: Nonfiction
function catalogTree(data, value = b => b.revenue) {
const nest = d3.group(data.books, b => SHELF[b.genre] ?? 'Nonfiction', b => b.genre);
return d3.hierarchy(nest) // a Map becomes the entry [undefined, map]
.sum(d => d.id ? value(d) : 0) // only books (the leaves) carry a value
.sort((a, b) => b.height - a.height || b.value - a.value);
}
const nodeName = n => n.depth === 0 ? 'BookNest' : n.children ? n.data[0] : n.data.title;
const data = prepareSales(SALES), svg = d3.select('svg');
function draw(field) {
const root = catalogTree(data, b => b[field]);
const nodes = [];
root.eachBefore(n => nodes.push(n)); // 15 nodes, parents before children
const fmt = field === 'revenue' ? d3.format('$,.0f') : d3.format(',');
const x = d3.scaleLinear([0, root.value], [0, 190]);
const row = svg.selectAll('g.node').data(nodes, n => nodeName(n)).join(enter => {
const g = enter.append('g').attr('class', 'node');
g.append('rect').attr('height', 14).attr('y', -10);
g.append('text').attr('class', 'name');
g.append('text').attr('class', 'meta').attr('fill', '#78909c');
return g;
}).attr('transform', (n, i) => `translate(0, ${16 + i * 21})`);
row.select('rect').attr('x', 330).attr('fill', n => n.children ? '#b0bec5' : n.data.color)
.transition().attr('width', n => x(n.value));
row.select('.name').attr('x', n => 4 + n.depth * 22).attr('font-weight', n => n.children ? 'bold' : null)
.text(n => `${n.children ? '▾' : '•'} ${nodeName(n)}`);
row.select('.meta').attr('x', 250).text(n => `d${n.depth} h${n.height}`);
row.selectAll('text.v').data(n => [n]).join('text').attr('class', 'v')
.attr('x', n => 334 + x(n.value)).text(n => fmt(n.value));
// Parent links: a vertical line from each parent down to its last child
svg.selectAll('path.link').data(root.links()).join('path').attr('class', 'link').lower()
.attr('fill', 'none').attr('stroke', '#cfd8dc')
.attr('d', ({ source, target }) => {
const y0 = 16 + nodes.indexOf(source) * 21, y1 = 16 + nodes.indexOf(target) * 21, x0 = 8 + source.depth * 22;
return `M${x0},${y0 + 3}V${y1 - 4}H${x0 + 12}`;
});
}
d3.selectAll('input[name=v]').on('change', e => draw(e.target.value));
draw('revenue');
</script>