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 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).
import { createShuffle } from 'fast-shuffle' // note the change
const letters = ['a', 'b', 'c', 'd', 'e']
const shuffleRed = createShuffle(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 = createShuffle(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' ]The parameters are also curried, so it can be used in pipelines.
import { createShuffle } from 'fast-shuffle'
const randomCapitalLetter =
['a', 'b', 'c', 'd', 'e', 'f'] // :: () -> [a]
|> createShuffle(Math.random), // :: [a] -> [a]
|> _ => _[0] // :: [a] -> a
|> _ => _.toUpperCase() // :: a -> aIf 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.
import { SHUFFLE_DECK } from './actions'
import { createShuffle } from 'fast-shuffle'
const initialState = {
...
deck: ['♣', '♦', '♥', '♠'],
randomizer: Date.now()
}
const dealerApp = (state = initialState, action) => {
switch (action.type) {
...
case SHUFFLE_DECK:
const [ deck, randomizer ] = createShuffle([state.deck, state.randomizer])
return {
...state,
deck,
randomizer,
}
...
default:
return state
}
}Why not use existing libraries?
-
It doesn't mutate your source array, so it's safe for Redux reducers.
-
The parameters are curried in the correct order, so you can use it within
|>or Ramda pipes. -
You can make it a deterministic pure function, useful for shuffling in tests.
-
It's stupid-fast and scales to large arrays without breaking a sweat.