有效地挑个随机元素从PHP数组（不含洗牌） [英] Efficiently pick n random elements from PHP array (without shuffle)

问题描述

我有以下的code接 $ N 从PHP中的数组 $阵列元素：

 洗牌（$数组）;
$结果= array_splice（$数组，0，$ N）;
 

给定一个大阵，但只有少数几个元素（例如 5 出的 10000 ），这是比较慢，所以我想优化它，使得并不是所有的元素都被打乱。该值必须是唯一的。

我在寻找FO最高效的替代品。我们可以假设， $阵列有没有重复，是 0 -indexed。

解决方案

  $ randomArray = [];
而（计数（$ randomArray）小于5））{
  $ randomKey = mt_rand（0，计数（$数组）-1）;
  $ randomArray [$ randomKey] = $阵列[$ randomKey];
}
 

这将提供没有重复并很快正好5个元素。钥匙将是preserved。

的注：你必须确保$阵列有5个或更多的元素，或添加某种检查，以prevent无限循环的

。

I have the following code to pick $n elements from an array $array in PHP:

shuffle($array);
$result = array_splice($array, 0, $n);

Given a large array but only a few elements (for example 5 out of 10000), this is relatively slow, so I would like to optimize it such that not all elements have to be shuffled. The values must be unique.

I'm looking fo the most performant alternative. We can assume that $array has no duplicates and is 0-indexed.

解决方案

$randomArray = [];
while (count($randomArray) < 5)) {
  $randomKey = mt_rand(0, count($array)-1);
  $randomArray[$randomKey] = $array[$randomKey];
}

This will provide exactly 5 elements with no duplicates and very quickly. The keys will be preserved.

Note: You'd have to make sure $array had 5 or more elements or add some sort of check to prevent an endless loop.

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