🚧 progress: Importing existing sources, tests.

Also added a code sample and reversed argument order.

Author: make-github-pseudonymous-again

README.md

@@ -4,13 +4,16 @@
 Iterable windowed iteration for JavaScript.
 See [docs](https://iterable-iterator.github.io/window/index.html).
 
-> :building_construction: Caveat emptor! This is work in progress. Code may be
-> working. Documentation may be present. Coherence may be. Maybe.
-
 > :warning: Depending on your environment, the code may require
 > `regeneratorRuntime` to be defined, for instance by importing
 > [regenerator-runtime/runtime](https://www.npmjs.com/package/regenerator-runtime).
 
+```js
+import {window} from '@iterable-iterator/window';
+
+for (const [x, y] of window(2, 'abcde')) ... ; // ab bc cd de
+```
+
 [![License](https://img.shields.io/github/license/iterable-iterator/window.svg)](https://raw.githubusercontent.com/iterable-iterator/window/main/LICENSE)
 [![Version](https://img.shields.io/npm/v/@iterable-iterator/window.svg)](https://www.npmjs.org/package/@iterable-iterator/window)
 [![Tests](https://img.shields.io/github/workflow/status/iterable-iterator/window/ci:test?event=push&label=tests)](https://github.com/iterable-iterator/window/actions/workflows/ci:test.yml?query=branch:main)

package.json

@@ -59,12 +59,17 @@
     "release": "np --message ':hatching_chick: release: Bumping to v%s.'",
     "test": "ava"
   },
-  "dependencies": {},
+  "dependencies": {
+    "@iterable-iterator/iter": "^0.0.2",
+    "@iterable-iterator/range": "^1.0.0"
+  },
   "devDependencies": {
     "@babel/core": "7.14.0",
     "@babel/preset-env": "7.14.0",
     "@babel/register": "7.13.16",
     "@commitlint/cli": "12.1.1",
+    "@iterable-iterator/list": "^0.0.2",
+    "@iterable-iterator/zip": "^0.0.2",
     "@js-library/commitlint-config": "0.0.4",
     "ava": "3.15.0",
     "babel-plugin-transform-remove-console": "6.9.4",

src/index.js

@@ -1,2 +1 @@
-const answer = 42;
-export default answer;
+export {default as window} from './window.js';

src/window.js

@@ -0,0 +1,45 @@
+import {iter} from '@iterable-iterator/iter';
+import {range} from '@iterable-iterator/range';
+
+/**
+ * Yields tuples that contain the current element of the input iterable and the
+ * next <code>n-1</code> elements of the input iterable.
+ *
+ * @example
+ * window( range( 100 ) , 2 ) ;
+ * // is equivalent to
+ * zip( range( 100 ) , range( 1 , 100 ) ) ;
+ *
+ * @param {number} n - The window size.
+ * @param {Iterable} iterable - The input iterable.
+ * @returns {IterableIterator<Array>}
+ */
+export default function* window(n, iterable) {
+	// Could have an implementation using a deque
+	// that doesn't slice (and thus allocate a new
+	// vector everytime). Though the yield object
+	// could not be modified by the caller in that case.
+
+	const iterator = iter(iterable);
+
+	let tuple = [];
+
+	// eslint-disable-next-line no-unused-vars
+	for (const i of range(n)) {
+		const current = iterator.next();
+
+		if (current.done) {
+			return;
+		}
+
+		tuple.push(current.value);
+	}
+
+	yield tuple;
+
+	for (const value of iterator) {
+		tuple = tuple.slice(1);
+		tuple.push(value);
+		yield tuple;
+	}
+}

test/src/api.js

@@ -0,0 +1,26 @@
+import test from 'ava';
+
+import {range} from '@iterable-iterator/range';
+import {zip} from '@iterable-iterator/zip';
+import {list} from '@iterable-iterator/list';
+
+import {window} from '../../src/index.js';
+
+test('compare to zip output', (t) => {
+	const A = window(2, range(100));
+	const B = zip(range(100), range(1, 100));
+	t.deepEqual(list(A), list(B));
+});
+
+test('n !| N', (t) => {
+	const C = window(3, range(4));
+	t.deepEqual(list(C), [
+		[0, 1, 2],
+		[1, 2, 3],
+	]);
+});
+
+test('window larger than input', (t) => {
+	const D = window(3, range(2));
+	t.deepEqual(list(D), [], 'empty');
+});