stack

Author: mbostock

src/index.js

@@ -15,3 +15,4 @@ export {Text, text, textX, textY} from "./marks/text.js";
 export {TickX, TickY, tickX, tickY} from "./marks/tick.js";
 export {bin1, bin2} from "./transforms/bin.js";
 export {group1, group2} from "./transforms/group.js";
+export {stackX, stackY} from "./transforms/stack.js";

src/mark.js

@@ -77,14 +77,12 @@ export class Mark {
 
 // TODO Type coercion?
 function Channel(data, {scale, type, value}) {
-  let label;
-  if (typeof value === "function") {
-    label = value.label;
-    value = Array.from(data, value);
-  } else {
-    value = arrayify(value);
-  }
-  return {scale, type, value, label};
+  return {
+    scale,
+    type,
+    value: typeof value === "function" ? Array.from(data, value) : arrayify(value),
+    label: value ? value.label : undefined
+  };
 }
 
 // This allows transforms to behave equivalently to channels.

src/transforms/stack.js

@@ -0,0 +1,42 @@
+import {valueof} from "../mark";
+
+// TODO configurable series order
+export function stackX(data, {x, y, ...options}) {
+  const X = valueof(data, x);
+  const Y = valueof(data, y);
+  const n = X.length;
+  const X0 = new Map();
+  const X1 = new Float64Array(n);
+  const X2 = new Float64Array(n);
+  for (let i = 0; i < n; ++i) {
+    const k = Y[i] && Y[i].valueOf();
+    const x1 = X1[i] = X0.has(k) ? X0.get(k) : 0;
+    const x2 = X2[i] = x1 + +X[i];
+    X0.set(k, isNaN(x2) ? x1 : x2);
+  }
+  return [data, {...options, x1: maybeLabel(X1, x), x2: X2, y: maybeLabel(Y, y)}];
+}
+
+// TODO configurable series order
+export function stackY(data, {x, y, ...options}) {
+  const X = valueof(data, x);
+  const Y = valueof(data, y);
+  const n = X.length;
+  const Y0 = new Map();
+  const Y1 = new Float64Array(n);
+  const Y2 = new Float64Array(n);
+  for (let i = 0; i < n; ++i) {
+    const k = X[i] && X[i].valueOf();
+    const y1 = Y1[i] = Y0.has(k) ? Y0.get(k) : 0;
+    const y2 = Y2[i] = y1 + +Y[i];
+    Y0.set(k, isNaN(y2) ? y1 : y2);
+  }
+  return [data, {...options, x: maybeLabel(X, x), y1: maybeLabel(Y1, y), y2: Y2}];
+}
+
+// If x is a labeled value, propagate the label to the returned value array.
+function maybeLabel(X, x) {
+  const label = typeof x === "string" ? x : x ? x.label : undefined;
+  if (label !== undefined) X.label = label;
+  return X;
+}