A spine plot (spineplot) is a stacked bar chart where bar widths are proportional to the marginal frequency of one categorical variable and the subdivisions within each bar show the conditional distribution of a second categorical variable. All bars are normalized to the same height (100%), so visual comparison focuses on how the conditional proportions shift across categories. It is a one-dimensional specialization of mosaic plots and excels at revealing associations between two categorical variables in contingency table data.
// anyplot.ai
// bar-spine: Spine Plot for Two-Variable Proportions
// Library: d3 7.9.0 | JavaScript 22.23.2
// Quality: 92/100 | Created: 2026-09-02
const t = window.ANYPLOT_TOKENS;
const { width, height } = window.ANYPLOT_SIZE;
// Theme-adaptive muted anchor (not shipped in ANYPLOT_TOKENS — see default-style-guide.md)
const MUTED = t.theme === "dark" ? "#A8A79F" : "#6B6A63";
const LIGHT_TXT = "#FFFDF6";
const DARK_TXT = "#1A1A17";
// --- WCAG contrast helpers (pick readable in-segment label color) -----------
const luminance = (hex) => {
const c = hex.replace("#", "");
const [r, g, b] = [0, 2, 4].map((i) => parseInt(c.substr(i, 2), 16) / 255);
const lin = (v) => (v <= 0.04045 ? v / 12.92 : Math.pow((v + 0.055) / 1.055, 2.4));
return 0.2126 * lin(r) + 0.7152 * lin(g) + 0.0722 * lin(b);
};
const contrast = (hexA, hexB) => {
const [la, lb] = [luminance(hexA), luminance(hexB)];
const [hi, lo] = la > lb ? [la, lb] : [lb, la];
return (hi + 0.05) / (lo + 0.05);
};
const textColorFor = (bgHex) =>
contrast(bgHex, DARK_TXT) >= contrast(bgHex, LIGHT_TXT) ? DARK_TXT : LIGHT_TXT;
// --- Data: clinical trial outcome by dosage group (in-memory, deterministic) -
const data = [
{ category: "Placebo", n: 120, counts: { Improved: 24, "No Change": 60, Worsened: 36 } },
{ category: "Low Dose", n: 95, counts: { Improved: 43, "No Change": 38, Worsened: 14 } },
{ category: "Medium Dose", n: 150, counts: { Improved: 98, "No Change": 37, Worsened: 15 } },
{ category: "High Dose", n: 80, counts: { Improved: 56, "No Change": 16, Worsened: 8 } },
];
// Improved/No Change/Worsened read as good/neutral/bad — semantic exception (default-style-guide.md)
const fillKeys = ["Improved", "No Change", "Worsened"];
const fillColor = { Improved: t.palette[0], "No Change": MUTED, Worsened: t.palette[4] };
// --- Layout --------------------------------------------------------------
const margin = { top: 155, right: 60, bottom: 115, left: 90 };
const iw = width - margin.left - margin.right;
const ih = height - margin.top - margin.bottom;
// Bar width proportional to marginal count n; segments stacked to 100 %.
const grandTotal = d3.sum(data, (d) => d.n);
let cursor = 0;
const bars = data.map((d) => {
const barWidth = (d.n / grandTotal) * iw;
const x0 = cursor;
cursor += barWidth;
let stack = 0;
const segments = fillKeys.map((key) => {
const pct = (d.counts[key] / d.n) * 100;
const seg = { key, pct, y0: stack, y1: stack + pct };
stack += pct;
return seg;
});
return { ...d, x0, barWidth, segments };
});
const y = d3.scaleLinear().domain([0, 100]).range([ih, 0]);
// --- SVG mount -------------------------------------------------------------
const svg = d3.select("#container").append("svg").attr("width", width).attr("height", height);
const g = svg.append("g").attr("transform", `translate(${margin.left},${margin.top})`);
// --- Y-axis (cumulative share) + gridlines ----------------------------------
const yAxis = g
.append("g")
.call(
d3
.axisLeft(y)
.tickValues([0, 25, 50, 75, 100])
.tickFormat((v) => `${v}%`)
.tickSize(-iw)
);
yAxis.selectAll("text").attr("fill", t.inkSoft).style("font-size", "14px").attr("x", -10);
yAxis.selectAll("line").attr("stroke", t.grid).attr("stroke-width", 1);
yAxis.select(".domain").remove();
g.append("text")
.attr("x", -ih / 2)
.attr("y", -62)
.attr("transform", "rotate(-90)")
.attr("text-anchor", "middle")
.attr("fill", t.inkSoft)
.style("font-size", "15px")
.text("Share of group");
// --- Spine bars --------------------------------------------------------------
const barGroups = g
.selectAll(".bar")
.data(bars)
.join("g")
.attr("transform", (d) => `translate(${d.x0},0)`);
// Segments + in-segment percentage labels (barWidth is per-group, so both are
// drawn together in one pass over the bound bar datum).
barGroups.each(function (bar) {
const group = d3.select(this);
group
.selectAll("rect")
.data(bar.segments)
.join("rect")
.attr("x", 0)
.attr("y", (seg) => y(seg.y1))
.attr("width", bar.barWidth)
.attr("height", (seg) => y(seg.y0) - y(seg.y1))
.attr("fill", (seg) => fillColor[seg.key])
.attr("stroke", t.pageBg)
.attr("stroke-width", 1.5);
bar.segments.forEach((seg) => {
const segHeight = y(seg.y0) - y(seg.y1);
if (segHeight < 34 || bar.barWidth < 50) return;
group
.append("text")
.attr("x", bar.barWidth / 2)
.attr("y", (y(seg.y1) + y(seg.y0)) / 2)
.attr("text-anchor", "middle")
.attr("dominant-baseline", "central")
.attr("fill", textColorFor(fillColor[seg.key]))
.style("font-size", "15px")
.style("font-weight", "600")
.text(`${Math.round(seg.pct)}%`);
});
});
// Baseline under the bars.
g.append("line")
.attr("x1", 0)
.attr("x2", iw)
.attr("y1", ih)
.attr("y2", ih)
.attr("stroke", t.inkSoft)
.attr("stroke-width", 1);
// --- X-axis: category name + group size, centered under each variable-width bar
barGroups.each(function (bar) {
const group = d3.select(this);
const cx = bar.barWidth / 2;
group
.append("text")
.attr("x", cx)
.attr("y", ih + 32)
.attr("text-anchor", "middle")
.attr("fill", t.ink)
.style("font-size", "16px")
.style("font-weight", "600")
.text(bar.category);
group
.append("text")
.attr("x", cx)
.attr("y", ih + 54)
.attr("text-anchor", "middle")
.attr("fill", t.inkSoft)
.style("font-size", "13px")
.text(`n = ${bar.n}`);
});
g.append("text")
.attr("x", iw / 2)
.attr("y", ih + 88)
.attr("text-anchor", "middle")
.attr("fill", t.inkSoft)
.style("font-size", "13px")
.style("font-style", "italic")
.text("Bar width is proportional to group size (n)");
// --- Legend (measured with getBBox for exact centering) ---------------------
const legend = svg.append("g");
const legendItems = fillKeys.map((key) => {
const item = legend.append("g");
item
.append("rect")
.attr("width", 22)
.attr("height", 22)
.attr("rx", 3)
.attr("fill", fillColor[key]);
item
.append("text")
.attr("x", 32)
.attr("y", 16)
.attr("fill", t.ink)
.style("font-size", "15px")
.text(key);
return { node: item, width: item.node().getBBox().width };
});
const gap = 40;
const legendWidth = d3.sum(legendItems, (d) => d.width) + gap * (legendItems.length - 1);
let lx = (width - legendWidth) / 2;
legendItems.forEach((d) => {
d.node.attr("transform", `translate(${lx},96)`);
lx += d.width + gap;
});
// --- Title -------------------------------------------------------------------
const titleText = "Clinical Trial Outcome by Dosage · bar-spine · javascript · d3 · anyplot.ai";
const titleFontSize = Math.max(14, Math.round(22 * Math.min(1, 67 / titleText.length)));
svg
.append("text")
.attr("x", width / 2)
.attr("y", 46)
.attr("text-anchor", "middle")
.attr("fill", t.ink)
.style("font-size", `${titleFontSize}px`)
.style("font-weight", "600")
.text(titleText);
Runnable source as JSON, for any HTTP client: https://api.anyplot.ai/specs/bar-spine/d3/code. Any spec id and library id listed in llms-full.txt fit the same URL shape; every URL below is complete and callable.
{
"spec_id": "bar-spine",
"language": "javascript",
"library": "d3",
"page": "https://anyplot.ai/bar-spine/javascript/d3",
"hub": "https://anyplot.ai/bar-spine",
"code_json": "https://api.anyplot.ai/specs/bar-spine/d3/code",
"spec_json": "https://api.anyplot.ai/specs/bar-spine",
"render_light_png": "https://storage.googleapis.com/anyplot-images/plots/bar-spine/javascript/d3/plot-light.png",
"render_dark_png": "https://storage.googleapis.com/anyplot-images/plots/bar-spine/javascript/d3/plot-dark.png",
"interactive_light_html": "https://storage.googleapis.com/anyplot-images/plots/bar-spine/javascript/d3/plot-light.html",
"interactive_dark_html": "https://storage.googleapis.com/anyplot-images/plots/bar-spine/javascript/d3/plot-dark.html",
"quality_score": 92.0,
"license": "MIT",
"guide": "https://anyplot.ai/llms.txt"
}Part of Spine Plot for Two-Variable Proportions on anyplot.ai.