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

import { shuffle } from 'fast-shuffle'

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

const shuffledDeck = shuffle(sortedDeck)
// [ '3♥', '3♦', 'K♥', '6♦', 'J♣', '5♠', 'A♠', ...

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

import { shuffle } from 'fast-shuffle'

const randomCapitalLetter =
  ['a', 'b', 'c', 'd', 'e', 'f']   // :: () -> [a]
  |> shuffle,                      // :: [a] -> [a]
  |> _ => _[0]                     // :: [a] -> a
  |> _ => _.toUpperCase()          // :: a -> a

The named shuffle export seen above uses Math.random for entropy. If you import it without the brackets, you'll get a deterministic shuffler which takes an int for its random seed (e.g. Date.now()).

import shuffle from 'fast-shuffle' // note the change

const letters = ['a', 'b', 'c', 'd', 'e']
const shuffleRed = shuffle(12345)
shuffleRed(letters) // [ 'a', 'b', 'c', 'd', 'e' ]
shuffleRed(letters) // [ 'a', 'd', 'b', 'e', 'c' ]
shuffleRed(letters) // [ 'c', 'a', 'e', 'b', 'd' ]
shuffleRed(letters) // [ 'b', 'c', 'e', 'a', 'd' ]

const shuffleBlue = shuffle(12345)
shuffleBlue(letters) // [ 'a', 'b', 'c', 'd', 'e' ]
shuffleBlue(letters) // [ 'a', 'd', 'b', 'e', 'c' ]
shuffleBlue(letters) // [ 'c', 'a', 'e', 'b', 'd' ]
shuffleBlue(letters) // [ 'b', 'c', 'e', 'a', 'd' ]

If you give it an array of your array and a random seed, you'll get a shuffled array and a new random seed back. This is a pure function, so you can use it in your Redux reducers.

import { SHUFFLE_DECK } from './actions'
import shuffle from 'fast-shuffle'

const initialState = {
  ...
  deck: ['♣', '♦', '♥', '♠'],
  randomizer: Date.now()
}

const dealerApp = (state = initialState, action) => {
  switch (action.type) {
    ...
    case SHUFFLE_DECK:
      const [ deck, randomizer ] = shuffle([state.deck, state.randomizer])
      return {
        ...state,
        deck,
        randomizer,
      }
    ...
    default:
      return state
  }
}

Shuffle doesn't mutate the original array, instead it gives you back a shallow copy. This is important for React and performance reasons.

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

4. You can BYO-RNG.