Add an error message when using a given stacking order (as an array) …

…without a z channel (observablehq#1209)

closes observablehq#1208

src/transforms/stack.js

@@ -325,6 +325,7 @@ function orderGiven(domain) {
 // O that can be used with applyOrder to sort stacks. Note that this is a series
 // order: it will be consistent across stacks.
 function orderZDomain(Z, domain) {
+  if (!Z) throw new Error("missing channel: z");
   domain = new InternMap(domain.map((d, i) => [d, i]));
   return Z.map((z) => domain.get(z));
 }

test/plots/index.js

@@ -141,6 +141,7 @@ export {default as moviesProfitByGenre} from "./movies-profit-by-genre.js";
 export {default as moviesRatingByGenre} from "./movies-rating-by-genre.js";
 export {default as musicRevenue} from "./music-revenue.js";
 export {default as multiplicationTable} from "./multiplication-table.js";
+export {default as npmVersions} from "./npm-versions.js";
 export {default as ordinalBar} from "./ordinal-bar.js";
 export {default as penguinAnnotated} from "./penguin-annotated.js";
 export {default as penguinCulmen} from "./penguin-culmen.js";

test/plots/npm-versions.js

@@ -0,0 +1,91 @@
+import * as Plot from "@observablehq/plot";
+
+export default async function () {
+  const versions = [
+    {version: "0.5.0", downloads: 7},
+    {version: "0.5.1", downloads: 6},
+    {version: "0.5.2", downloads: 7},
+    {version: "0.6.0", downloads: 7},
+    {version: "0.6.1", downloads: 8},
+    {version: "0.6.2", downloads: 4},
+    {version: "0.7.0", downloads: 4},
+    {version: "0.7.1", downloads: 2434},
+    {version: "0.8.0", downloads: 6},
+    {version: "0.8.1", downloads: 77},
+    {version: "1.0.0", downloads: 245},
+    {version: "1.0.1", downloads: 9712},
+    {version: "1.0.2", downloads: 2461},
+    {version: "1.0.3", downloads: 18},
+    {version: "1.1.0", downloads: 103},
+    {version: "1.1.1", downloads: 758},
+    {version: "1.2.0", downloads: 6845},
+    {version: "1.2.1", downloads: 88628},
+    {version: "1.2.2", downloads: 26},
+    {version: "1.2.3", downloads: 4},
+    {version: "1.2.4", downloads: 1313149},
+    {version: "2.0.0", downloads: 765},
+    {version: "2.0.1", downloads: 6},
+    {version: "2.0.2", downloads: 75},
+    {version: "2.0.3", downloads: 871},
+    {version: "2.1.0", downloads: 16},
+    {version: "2.2.0", downloads: 1212},
+    {version: "2.3.0", downloads: 254},
+    {version: "2.3.1", downloads: 2538},
+    {version: "2.3.2", downloads: 124},
+    {version: "2.3.3", downloads: 37650},
+    {version: "2.4.0", downloads: 48693},
+    {version: "2.5.0", downloads: 12756},
+    {version: "2.5.1", downloads: 743},
+    {version: "2.6.0", downloads: 1125},
+    {version: "2.7.0", downloads: 509},
+    {version: "2.7.1", downloads: 3234},
+    {version: "2.8.0", downloads: 24886},
+    {version: "2.9.0", downloads: 1803},
+    {version: "2.9.1", downloads: 19828},
+    {version: "2.10.0", downloads: 414},
+    {version: "2.11.0", downloads: 34090},
+    {version: "2.12.0", downloads: 8686},
+    {version: "2.12.1", downloads: 1350944},
+    {version: "3.0.0", downloads: 5},
+    {version: "3.0.1", downloads: 13942},
+    {version: "3.0.2", downloads: 12132},
+    {version: "3.0.3", downloads: 24},
+    {version: "3.0.4", downloads: 26361},
+    {version: "3.1.0", downloads: 349},
+    {version: "3.1.1", downloads: 278205},
+    {version: "3.1.2", downloads: 125},
+    {version: "3.1.3", downloads: 375},
+    {version: "3.1.4", downloads: 3550},
+    {version: "3.1.5", downloads: 2004},
+    {version: "3.1.6", downloads: 89445},
+    {version: "3.2.0", downloads: 490566},
+    {version: "3.2.1", downloads: 438869}
+  ];
+  const order = Plot.valueof(versions, "version");
+  return Plot.plot({
+    x: {grid: true},
+    y: {reverse: true},
+    color: {scheme: "rainbow", domain: order},
+    marks: [
+      Plot.barX(versions, {
+        x: "downloads",
+        y: (d) => parseInt(d.version),
+        order,
+        fill: "version",
+        title: "version",
+        insetLeft: 1
+      }),
+      Plot.text(
+        versions,
+        Plot.stackX({
+          x: "downloads",
+          y: (d) => parseInt(d.version),
+          order,
+          text: (d) => (d.downloads > 50e3 ? d.version : ""),
+          z: "version"
+        })
+      ),
+      Plot.ruleX([0])
+    ]
+  });
+}