Array Shuffle

Sometimes you might need to shuffle an array. This utility shuffle function is based on the effective Fisher–Yates shuffle algorithm. Learn how it works in this video.

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function shuffle(arr) {
  const array = [...arr] // Consider a use of deep copy
  const lastIndex = array.length - 1

  // Start from the last element and swap one by one.
  for (let index = lastIndex; index > 0; index--) {
    // 1. Pick a random index among lower ones
    const randomIndex = Math.floor(Math.random() * (index + 1))
    // 2. Swap elements
    ;[array[index], array[randomIndex]] = [array[randomIndex], array[index]]
  }

  return array
}

And here is the Lodash implementation that uses a while-loop:

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function shuffleSelf(array, size) {
  var index = -1,
    length = array.length,
    lastIndex = length - 1

  size = size === undefined ? length : size
  while (++index < size) {
    var rand = baseRandom(index, lastIndex),
      value = array[rand]

    array[rand] = array[index]
    array[index] = value
  }
  array.length = size
  return array
}