从阵列采样的随机子集 [英] Sampling a random subset from an array

问题描述

什么是从在JavaScript数组采取随机抽样，无需更换一个干净的方式？因此，假设有一个数组

What is a clean way of taking a random sample, without replacement from an array in javascript? So suppose there is an array

x = [1,2,3,4,5,6,7,8,9,10,11,12,13,14,15]

和我想随机抽取5独特的价值观;即产生长度为5的随机子集生成一个随机抽样人可以这样做：

and I want to randomly sample 5 unique values; i.e. generate a random subset of length 5. To generate one random sample one could do something like:

x[Math.floor(Math.random()*x.length)];

但是，如果这样做多次，有一个多次敛同一条目的危险。

But if this is done multiple times, there is a risk of a grabbing the same entry multiple times.

推荐答案

我建议使用的费雪耶茨洗牌并采取切片：

I suggest shuffling a copy of the array using the Fisher-Yates shuffle and taking a slice:

function getRandomSubarray(arr, size) {
    var shuffled = arr.slice(0), i = arr.length, temp, index;
    while (i--) {
        index = Math.floor((i + 1) * Math.random());
        temp = shuffled[index];
        shuffled[index] = shuffled[i];
        shuffled[i] = temp;
    }
    return shuffled.slice(0, size);
}

var x = [1,2,3,4,5,6,7,8,9,10,11,12,13,14,15];
var fiveRandomMembers = getRandomSubarray(x, 5);

请注意，这不会是获得了大阵中的一小随机子集，因为它打乱了整个阵列不必要的最有效的方法。为了获得更好的性能，你可以做一个部分，而不是洗牌：

Note that this will not be the most efficient method for getting a small random subset of a large array because it shuffles the whole array unnecessarily. For better performance you could do a partial shuffle instead:

function getRandomSubarray(arr, size) {
    var shuffled = arr.slice(0), i = arr.length, min = i - size, temp, index;
    while (i-- > min) {
        index = Math.floor((i + 1) * Math.random());
        temp = shuffled[index];
        shuffled[index] = shuffled[i];
        shuffled[i] = temp;
    }
    return shuffled.slice(min);
}

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