Fast Shuffle

A fast, side-effect-free, and O(n) array shuffle that's safe for functional programming and use within Redux reducers.

Usage

npm install --save fast-shuffle

1import { shuffle } from 'fast-shuffle'
2
3const suits = ['♣', '♦', '♥', '♠']
4const faces = ['2', '3', '4', '5', '6', '7', '8', '9', 'T', 'J', 'Q', 'K', 'A']
5const sortedDeck = suits.map((suit) => faces.map((face) => face + suit)).flat()
6// [ '2♣', '3♣', '4♣', '5♣', '6♣', '7♣', '8♣', ...
7
8const shuffledDeck = shuffle(sortedDeck)
9// [ '3♥', '3♦', 'K♥', '6♦', 'J♣', '5♠', 'A♠', ...

The named shuffle export seen above uses Math.random for entropy. This is the easiest way to use the library, but it may be useful to create a purely functional shuffler which takes either a random seed which is used in a PCG for entropy, or a function (as seen here).

1import { createShuffle } from 'fast-shuffle' // note the change
2
3const letters = ['a', 'b', 'c', 'd', 'e']
4const shuffleRed = createShuffle(12345)
5shuffleRed(letters) // [ 'a', 'b', 'c', 'd', 'e' ]
6shuffleRed(letters) // [ 'a', 'd', 'b', 'e', 'c' ]
7shuffleRed(letters) // [ 'c', 'a', 'e', 'b', 'd' ]
8shuffleRed(letters) // [ 'b', 'c', 'e', 'a', 'd' ]
9
10const shuffleBlue = createShuffle(12345)
11shuffleBlue(letters) // [ 'a', 'b', 'c', 'd', 'e' ]
12shuffleBlue(letters) // [ 'a', 'd', 'b', 'e', 'c' ]
13shuffleBlue(letters) // [ 'c', 'a', 'e', 'b', 'd' ]
14shuffleBlue(letters) // [ 'b', 'c', 'e', 'a', 'd' ]

The parameters are also curried, so it can be used in pipelines.

1import { createShuffle } from 'fast-shuffle'
2
3const randomCapitalLetter =
4  ['a', 'b', 'c', 'd', 'e', 'f']   // :: () -> [a]
5  |> createShuffle(Math.random),       // :: [a] -> [a]
6  |> _ => _[0]                     // :: [a] -> a
7  |> _ => _.toUpperCase()          // :: a -> a

If you give it an array of your source array and a random seed, you'll get a shuffled array and a new random seed back. This is a pure function and the original array is not mutated, so you can use it in your Redux reducers. The returned, shuffled array is a shallow copy, so if you use this in React, you will often avoid unnecessary rerenders.

1import { SHUFFLE_DECK } from './actions'
2import { createShuffle } from 'fast-shuffle'
3
4const initialState = {
5  ...
6  deck: ['♣', '♦', '♥', '♠'],
7  randomizer: Date.now()
8}
9
10const dealerApp = (state = initialState, action) => {
11  switch (action.type) {
12    ...
13    case SHUFFLE_DECK:
14      const [ deck, randomizer ] = createShuffle([state.deck, state.randomizer])
15      return {
16        ...state,
17        deck,
18        randomizer,
19      }
20    ...
21    default:
22      return state
23  }
24}

Why not use existing libraries?

1. It doesn't mutate your source array, so it's safe for Redux reducers.

2. The parameters are curried in the correct order, so you can use it within |> or Ramda pipes.

3. You can make it a deterministic pure function, useful for shuffling in tests.

4. It's stupid-fast and scales to large arrays without breaking a sweat.