faceted stacks

Author: Fil

src/transforms/stack.js

@@ -11,8 +11,6 @@ export function stackY(data, {x, y, z, zOrder, offset, ...options}) {
   const Y = valueof(data, y);
   const n = X.length;
   const I = range(n);
-  const Yp = new InternMap();
-  const Yn = new InternMap();
   const Y1 = new Float64Array(n);
   const Y2 = new Float64Array(n);
 
@@ -23,41 +21,61 @@ export function stackY(data, {x, y, z, zOrder, offset, ...options}) {
     I.sort((i, j) => ascending(Z[i], Z[j]));
   }
 
-  // stack
-  for (const i of I) {
-    const k = X[i];
-    const v = +Y[i];
-    const [Y0, ceil, floor] = v < 0 ? [Yn, Y1, Y2] : [Yp ,Y2, Y1];
-    const y1 = floor[i] = Y0.has(k) ? Y0.get(k) : 0;
-    const y2 = ceil[i] = y1 + +Y[i];
-    Y0.set(k, isNaN(y2) ? y1 : y2);
-  }
-  
-  // offset
-  if (offset === "expand") {
-    for (const i of I) {
-      const k = X[i];
-      const floor = Yn.has(k) ? Yn.get(k) : 0;
-      const ceil = Yp.has(k) ? Yp.get(k) : 0;
-      const m = 1 / (ceil - floor || 1);
-      Y1[i] = m * (-floor + Y1[i]);
-      Y2[i] = m * (-floor + Y2[i]);
-    }
-  }
-  if (offset === "silhouette") {
-    for (const i of I) {
-      const k = X[i];
-      const floor = Yn.has(k) ? Yn.get(k) : 0;
-      const ceil = Yp.has(k) ? Yp.get(k) : 0;
-      const m = (ceil + floor) / 2;
-      Y1[i] -= m;
-      Y2[i] -= m;
+  const transform = (data, facets) => {
+    const index = [];
+    for (const facet of (facets === undefined ? [I] : facets)) {
+      const Yp = new InternMap();
+      const Yn = new InternMap();
+
+      // stack
+      for (const i of facet) {
+        const k = X[i];
+        const v = +Y[i];
+        const [Y0, ceil, floor] = v < 0 ? [Yn, Y1, Y2] : [Yp ,Y2, Y1];
+        const y1 = floor[i] = Y0.has(k) ? Y0.get(k) : 0;
+        const y2 = ceil[i] = y1 + +Y[i];
+        Y0.set(k, isNaN(y2) ? y1 : y2);
+      }
+
+      // offset
+      if (offset === "expand") {
+        for (const i of facet) {
+          const k = X[i];
+          const floor = Yn.has(k) ? Yn.get(k) : 0;
+          const ceil = Yp.has(k) ? Yp.get(k) : 0;
+          const m = 1 / (ceil - floor || 1);
+          Y1[i] = m * (-floor + Y1[i]);
+          Y2[i] = m * (-floor + Y2[i]);
+        }
+      }
+      if (offset === "silhouette") {
+        for (const i of facet) {
+          const k = X[i];
+          const floor = Yn.has(k) ? Yn.get(k) : 0;
+          const ceil = Yp.has(k) ? Yp.get(k) : 0;
+          const m = (ceil + floor) / 2;
+          Y1[i] -= m;
+          Y2[i] -= m;
+        }
+      }
+      // todo "wiggle"
+      
+      index.push(facet);
     }
-  }
-  // todo "wiggle"
+
+    return {index: facets === undefined ? I : index, data};
+  };
 
   const ym = Y1.map((y1, i) => (y1 + Y2[i]) / 2);
-  return [data, {...options, x: maybeLabel(X, x), y1: maybeLabel(Y1, y), y2: Y2, ym, z}];
+  return [data, {
+    ...options,
+    transform,
+    x: maybeLabel(X, x),
+    y1: maybeLabel(Y1, y),
+    y2: Y2,
+    ym,
+    z
+  }];
 }
 
 // If x is a labeled value, propagate the label to the returned value array.