🚧 progress(convolution): First draft.

Author: make-github-pseudonymous-again

README.md

@@ -4,13 +4,23 @@
 Iterable convolution for JavaScript.
 See [docs](https://iterable-iterator.github.io/convolution/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 {convolution} from '@iterable-iterator/convolution';
+
+const moving_average = [1/4, 1/4, 1/4, 1/4];
+convolution(moving_average, signal); // ...
+
+const first_derivative = [1, -1];
+convolution(first_derivative, signal); // ...
+
+const second_derivative = [1, -2, 1];
+convolution(second_derivative, signal); // ...
+```
+
 [![License](https://img.shields.io/github/license/iterable-iterator/convolution.svg)](https://raw.githubusercontent.com/iterable-iterator/convolution/main/LICENSE)
 [![Version](https://img.shields.io/npm/v/@iterable-iterator/convolution.svg)](https://www.npmjs.org/package/@iterable-iterator/convolution)
 [![Tests](https://img.shields.io/github/workflow/status/iterable-iterator/convolution/ci:test?event=push&label=tests)](https://github.com/iterable-iterator/convolution/actions/workflows/ci:test.yml?query=branch:main)

package.json

@@ -59,12 +59,24 @@
     "release": "np --message ':hatching_chick: release: Bumping to v%s.'",
     "test": "ava"
   },
-  "dependencies": {},
+  "dependencies": {
+    "@functional-abstraction/operator": "^1.0.4",
+    "@iterable-iterator/chain": "^1.0.0",
+    "@iterable-iterator/list": "^0.0.2",
+    "@iterable-iterator/map": "^0.1.0",
+    "@iterable-iterator/reduce": "^0.0.1",
+    "@iterable-iterator/repeat": "^0.0.1",
+    "@iterable-iterator/reversed": "^0.0.2",
+    "@iterable-iterator/window": "^0.0.3",
+    "@iterable-iterator/zip": "^0.0.2"
+  },
   "devDependencies": {
     "@babel/core": "7.14.0",
     "@babel/preset-env": "7.14.0",
     "@babel/register": "7.13.16",
     "@commitlint/cli": "12.1.1",
+    "@iterable-iterator/count": "^0.0.1",
+    "@iterable-iterator/slice": "^0.0.1",
     "@js-library/commitlint-config": "0.0.4",
     "ava": "3.15.0",
     "babel-plugin-transform-remove-console": "6.9.4",

src/convolution.js

@@ -0,0 +1,20 @@
+import {_window} from '@iterable-iterator/window';
+import {_chain} from '@iterable-iterator/chain';
+import {nrepeat} from '@iterable-iterator/repeat';
+import {list} from '@iterable-iterator/list';
+import {reversed} from '@iterable-iterator/reversed';
+import {map, starmap} from '@iterable-iterator/map';
+import {mul} from '@functional-abstraction/operator';
+import {_zip2} from '@iterable-iterator/zip';
+import {sum} from '@iterable-iterator/reduce';
+
+const convolution = (kernel, signal) => {
+	const rKernel = list(reversed(kernel));
+	const n = rKernel.length;
+	return map(
+		(slidingWindow) => sum(starmap(mul, _zip2(rKernel, slidingWindow))),
+		_window(n, _chain([nrepeat(0, n - 1), signal, nrepeat(0, n - 1)])),
+	);
+};
+
+export default convolution;

src/index.js

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

test/src/api.js

@@ -0,0 +1,30 @@
+import test from 'ava';
+
+import {list} from '@iterable-iterator/list';
+import {count} from '@iterable-iterator/count';
+import {take} from '@iterable-iterator/slice';
+import {convolution} from '../../src/index.js';
+
+test('https://betterexplained.com/articles/intuitive-convolution/#Part_1_Hospital_Analogy single-day treatment', (t) => {
+	const signal = [1, 2, 3, 4, 5];
+	const kernel = [3];
+	const result = list(convolution(kernel, signal));
+	const expected = [3, 6, 9, 12, 15];
+	t.deepEqual(result, expected);
+});
+
+test('https://betterexplained.com/articles/intuitive-convolution/#Part_1_Hospital_Analogy multi-day treatment', (t) => {
+	const signal = [1, 2, 3, 4, 5];
+	const kernel = [3, 2, 1];
+	const result = list(convolution(kernel, signal));
+	const expected = [3, 8, 14, 20, 26, 14, 5];
+	t.deepEqual(result, expected);
+});
+
+test('derivative of unit slope', (t) => {
+	const signal = count();
+	const kernel = [1, -1];
+	const result = list(take(convolution(kernel, signal), 5));
+	const expected = [0, 1, 1, 1, 1];
+	t.deepEqual(result, expected);
+});