2024 shuffle

// 뒤에서부터 시작하면서 자리를 바꿀 유닛을 무작위로 구해서 교체하는 방식
const shuffle = (arr) => {
  for (let unitIndex = arr.length - 1; unitIndex > 0; unitIndex--) {
    const swapIndex = Math.round(Math.random() * unitIndex);

    if (swapIndex === unitIndex) continue;
    [arr[swapIndex], arr[unitIndex]] = [arr[unitIndex], arr[swapIndex]];
  }
};

const arr = Array.from({ length: 10 }, (_, i) => i);
console.log(arr); // [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
shuffle(arr); // [7, 0, 5, 9, 1, 8, 6, 2, 4, 3]

shuffle.js

const compare = () => 0.5 - Math.random()
const shuffle = arr => arr.concat().sort(compare)

module.exports = shuffle

shuffle-2.js

const repeat = (arr, length) => {
  return Array
    .from({length}, () => arr)
    .reduce((acc, arr) => acc.concat(arr))
}

const rand = () => Math.random() - .5

const stepper = (max) => {
  let index = -1
  return () => {
    index = index == max ? 0 : index + 1
    return index
  }
}

const compare = (() => {
  const dataset = repeat([-1, 0, 1], 3)
  const next = stepper(dataset.length)
  dataset.sort(rand)
  return () => dataset[next()]
})()

const shuffle = arr => arr.slice().sort(compare)

module.exports = shuffle

shuffle-2-2.js

const repeat = (arr, length) => {
  return Array
    .from({length}, () => arr)
    .reduce((acc, arr) => acc.concat(arr))
}

const rand = () => Math.random() - .5

const stepper = (max) => {
  let index = -1
  return () => {
    index = index == max ? 0 : index + 1
    return index
  }
}

const compare = (() => {
  const dataset = repeat([-1, 0, 1], 3)
  const next = stepper(dataset.length)
  dataset.sort(rand)
  return () => dataset[next()]
})()

const shuffle = arr => arr.concat().sort(compare)

module.exports = shuffle

shuffle-3.js

const rand = () => Math.random() - .5 > 0 ? 1 : -1

const stepper = (max) => {
  let index = -1
  return () => {
    index = index == max ? 0 : index + 1
    return index
  }
}

const compare = (() => {
  const dataset = Array.from({length: 9}).map(rand)
  const next = stepper(dataset.length)
  return () => dataset[next()]
})()

const shuffle = arr => arr.slice().sort(compare)

module.exports = shuffle