保留原值

长度任意，保留原值，返回新数组。

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shuf = (arr) => Array.prototype.reduce.call(arr,(acc, el) => {
    acc.push(el)
    // Move following line to func top for Sattolo's
    let i = Math.floor(Math.random() * (acc.length))
    ;[acc[i], acc[acc.length - 1]] = [acc[acc.length - 1], acc[i]]
    return acc
},[])

要不顺便写个运气测试……？

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function looksRandom(shuf) {
    let rat = [0, 1, 2, 3, 4] // expected: 5! = 120 results
    // generate permutations
    let perms = permutation(rat)
    let attempts = perms.length * 2333
    let luck = {}
    for (let i = 0; i < attempts; i++)
        luck[shuf(rat).join(',')] = (luck[shuf(rat).join(',')] >>> 0) + 1
    for (j of perms)
        if (typeof luck[j.join(',')] === 'undefined') {
            console.log(j)
            return false
        }
    // stddev?
    console.log(luck)
    return "maybe"
}

looksRandom(shuf) // true
looksRandom((arr) => (arr.sort(() => Math.random() - 0.5), arr)) // sort(): ?????