groups respect the domain option

src/transforms/group.js

@@ -87,8 +87,8 @@ function group2(xv, yv, {z, fill, stroke, weight, domain, normalize, ...options}
           if (normalize === "facet") n = W ? sum(facet, i => W[i]) : facet.length;
           for (const [, I] of groups(facet, G, defined1)) {
             if (normalize === "z") n = W ? sum(I, i => W[i]) : I.length;
-            for (const [y, fy] of groups(I, Y, ydefined)) {
-              for (const [x, f] of groups(fy, X, xdefined)) {
+            for (const [y, fy] of groups(I, Y, ydefined, ydomain)) {
+              for (const [x, f] of groups(fy, X, xdefined, xdomain)) {
                 const l = W ? sum(f, i => W[i]) : f.length;
                 groupFacet.push(i++);
                 groupData.push(take(data, f));
@@ -133,6 +133,9 @@ function defined1([key]) {
   return defined(key);
 }
 
-export function groups(I, X, defined = defined1) {
-  return X ? sort(grouper(I, i => X[i]), first).filter(defined) : [[, I]];
+export function groups(I, X, defined = defined1, domain) {
+  if (!X) return [[, I]];
+  const G = grouper(I, i => X[i]);
+  return domain ? domain.map(x => [x, G.has(x) ? G.get(x) : []])
+                : sort(G, first).filter(defined);
 }

test/transforms/group-test.js

@@ -0,0 +1,36 @@
+import * as Plot from "@observablehq/plot";
+import tape from "tape-await";
+
+tape("groupX respects the domain option (#255)", test => {
+  const data = ["A", "A", "C"];
+  const options = {x: d => d, domain: ["C", "B", "A"]};
+  const mark = Plot.dot(data, Plot.groupX(options));
+  const A = mark.initialize();
+  test.deepEqual(A.index, [0, 1, 2]);
+  test.deepEqual(A.channels.find(d => d[0] === "x")[1].value, ["C", "B", "A"]);
+  test.deepEqual(A.channels.find(d => d[0] === "y")[1].value, [1, 0, 2]);
+});
+
+tape("groupY respects the domain option (#255)", test => {
+  const data = ["A", "A", "C"];
+  const options = {x: d => d, domain: ["C", "B", "A"]};
+  const mark = Plot.dot(data, Plot.groupY(options));
+  const A = mark.initialize();
+  test.deepEqual(A.index, [0, 1, 2]);
+  test.deepEqual(A.channels.find(d => d[0] === "y")[1].value, ["C", "B", "A"]);
+  test.deepEqual(A.channels.find(d => d[0] === "x")[1].value, [1, 0, 2]);
+});
+
+tape("group respects the domain option (#255)", test => {
+  const data = ["A", "A", "C", "A", "C"];
+  const options = {x: d => d, y: d => d, domain: ["C", "B", "A"]};
+  const mark = Plot.dot(data, Plot.group(options));
+  const A = mark.initialize();
+  test.deepEqual(A.index, [0, 1, 2, 3, 4, 5, 6, 7, 8]);
+  test.deepEqual(A.channels.find(d => d[0] === "fill")[1].value, [
+  //C, B, A
+    2, 0, 0, // C
+    0, 0, 0, // B
+    0, 0, 3  // A
+  ]);
+});

test/transforms/reduce-test.js

@@ -1,7 +1,7 @@
 import * as Plot from "@observablehq/plot";
 import tape from "tape-await";
 
-tape("baked-in reducer reduce as expected", test => {
+tape("baked-in reducers reduce as expected", test => {
   const data = [0, 1, 2, 4, 5, 9];
   testReducer(test, data, "deviation", Math.sqrt(10.7));
   testReducer(test, data, "max", 9);