expose window, normalize (#551)

* expose window, normalize

* Update test/plots/aapl-bollinger.js

Co-authored-by: Philippe Rivière <[email protected]>

* update test snapshot

Co-authored-by: Philippe Rivière <[email protected]>

Author: mbostock

README.md

@@ -1340,6 +1340,14 @@ Plot.mapY("cumsum", {y: d3.randomNormal()})
 
 Equivalent to Plot.map({y: *map*, y1: *map*, y2: *map*}, *options*), but ignores any of **y**, **y1**, and **y2** not present in *options*.
 
+#### Plot.normalize(*basis*)
+
+```js
+Plot.map({y: Plot.normalize("first")}, {x: "Date", y: "Close", stroke: "Symbol"})
+```
+
+Returns a normalize map method for the given *basis*, suitable for use with Plot.map.
+
 #### Plot.normalizeX(*basis*, *options*)
 
 ```js
@@ -1356,6 +1364,14 @@ Plot.normalizeY("first", {x: "Date", y: "Close", stroke: "Symbol"})
 
 Like [Plot.mapY](#plotmapymap-options), but applies the normalize map method with the given *basis*.
 
+#### Plot.window(*k*)
+
+```js
+Plot.map({y: Plot.window(24)}, {x: "Date", y: "Close", stroke: "Symbol"})
+```
+
+Returns a window map method for the given window size *k*, suitable for use with Plot.map. For additional options to the window transform, replace the number *k* with an object with properties *k*, *anchor*, or *reduce*.
+
 #### Plot.windowX(*k*, *options*)
 
 ```js

src/index.js

@@ -16,9 +16,9 @@ export {reverse} from "./transforms/reverse.js";
 export {sort} from "./transforms/sort.js";
 export {bin, binX, binY} from "./transforms/bin.js";
 export {group, groupX, groupY, groupZ} from "./transforms/group.js";
-export {normalizeX, normalizeY} from "./transforms/normalize.js";
+export {normalize, normalizeX, normalizeY} from "./transforms/normalize.js";
 export {map, mapX, mapY} from "./transforms/map.js";
-export {windowX, windowY} from "./transforms/window.js";
+export {window, windowX, windowY} from "./transforms/window.js";
 export {selectFirst, selectLast, selectMaxX, selectMaxY, selectMinX, selectMinY} from "./transforms/select.js";
 export {stackX, stackX1, stackX2, stackY, stackY1, stackY2} from "./transforms/stack.js";
 export {formatIsoDate, formatWeekday, formatMonth} from "./format.js";

src/transforms/normalize.js

@@ -13,7 +13,7 @@ export function normalizeY(basis, options) {
   return mapY(normalize(basis), options);
 }
 
-function normalize(basis) {
+export function normalize(basis) {
   if (basis === undefined) return normalizeFirst;
   if (typeof basis === "function") return normalizeBasis((I, S) => basis(take(S, I)));
   switch ((basis + "").toLowerCase()) {

src/transforms/window.js

@@ -11,7 +11,7 @@ export function windowY(windowOptions = {}, options) {
   return mapY(window(windowOptions), options);
 }
 
-function window(options = {}) {
+export function window(options = {}) {
   if (typeof options === "number") options = {k: options};
   let {k, reduce, shift, anchor = maybeShift(shift)} = options;
   if (!((k = Math.floor(k)) > 0)) throw new Error("invalid k");

test/output/aaplBollinger.svg

@@ -0,0 +1,20 @@
+import * as Plot from "@observablehq/plot";
+import * as d3 from "d3";
+
+export default async function() {
+  const AAPL = await d3.csv("data/aapl.csv", d3.autoType);
+  return Plot.plot({
+    y: {
+      grid: true
+    },
+    marks: [
+      Plot.areaY(AAPL, Plot.map({y1: bollinger(20, -2), y2: bollinger(20, 2)}, {x: "Date", y: "Close", fillOpacity: 0.2})),
+      Plot.line(AAPL, Plot.map({y: bollinger(20, 0)}, {x: "Date", y: "Close", stroke: "blue"})),
+      Plot.line(AAPL, {x: "Date", y: "Close", strokeWidth: 1})
+    ]
+  });
+}
+
+function bollinger(N, K) {
+  return Plot.window({k: N, reduce: Y => d3.mean(Y) + K * d3.deviation(Y), anchor: "end"});
+}

test/plots/aapl-bollinger.js

@@ -1,3 +1,4 @@
+export {default as aaplBollinger} from "./aapl-bollinger.js";
 export {default as aaplCandlestick} from "./aapl-candlestick.js";
 export {default as aaplChangeVolume} from "./aapl-change-volume.js";
 export {default as aaplClose} from "./aapl-close.js";