arrayShuffle (#1018)

* arrayShuffle

* Update packages/util/src/array/shuffle.spec.ts

* Update packages/util/src/array/shuffle.spec.ts

* Update packages/util/src/array/shuffle.ts

* Early return for length 1

CHANGELOG.md

@@ -1,5 +1,12 @@
 # CHANGELOG
 
+## master
+
+Changes:
+
+- Added `arrayShuffle(input)` to shuffle an array into a new output
+
+
 ## 6.9.1 Jun 19, 2021
 
 Changes:

packages/util/src/array/index.ts

@@ -9,3 +9,4 @@ export { arrayChunk } from './chunk';
 export { arrayFilter } from './filter';
 export { arrayFlatten } from './flatten';
 export { arrayRange } from './range';
+export { arrayShuffle } from './shuffle';

packages/util/src/array/shuffle.spec.ts

@@ -0,0 +1,31 @@
+// Copyright 2017-2021 @polkadot/util authors & contributors
+// SPDX-License-Identifier: Apache-2.0
+
+import { arrayRange, arrayShuffle } from '.';
+
+describe('arrayShuffle', (): void => {
+  it('returns an empty array as-is', (): void => {
+    expect(
+      arrayShuffle([])
+    ).toEqual([]);
+  });
+
+  it('returns a single array as-is', (): void => {
+    expect(
+      arrayShuffle([100])
+    ).toEqual([100]);
+  });
+
+  it('shuffles an array', (): void => {
+    const inp = arrayRange(100);
+    const out = arrayShuffle(inp);
+
+    expect(inp).toHaveLength(out.length);
+    expect(
+      inp.filter((v) => !out.includes(v))
+    ).toEqual([]);
+    expect(
+      JSON.stringify(inp)
+    ).not.toEqual(JSON.stringify(out));
+  });
+});

packages/util/src/array/shuffle.ts

@@ -0,0 +1,21 @@
+// Copyright 2017-2021 @polkadot/util authors & contributors
+// SPDX-License-Identifier: Apache-2.0
+
+export function arrayShuffle <T> (input: T[]): T[] {
+  const result = [...input];
+  let curr = result.length;
+
+  if (curr === 1) {
+    return result;
+  }
+
+  while (curr !== 0) {
+    const rand = Math.floor(Math.random() * curr);
+
+    curr--;
+
+    [result[curr], result[rand]] = [result[rand], result[curr]];
+  }
+
+  return result;
+}