从一个数组PHP获取随机值的一个子集 [英] Get a subset of random values from an array php

问题描述

与10K值的数组开始。我想从它随机得到1000个值并把它们放到另一个数组。

Starting with an array with 10K values. I want to randomly get 1000 values from it and put them into another array.

现在，我使用的是循环得到的值，但我要挑1000个值，而不必循环1000次。所述array_slice功能的工作原理，但它不给随机值。什么是此任务的正确的（最有效）的功能。

Right now, I am using a for loop to get the values, but I want to pick 1000 values and not have to loop 1000 times. The array_slice function works, but it doesn't give random values. What is the correct (most efficient) function for this task.

在code现在是

$seedkeys = (...array.....);

for ($i=0; $i<1000; $i++) {
        $random = array_rand($seedkeys);  
    $randseed[$i] = $seedkeys[$random];   

}//for close

TIA

推荐答案

好了，有几个选择。我不知道这是最快的，因为你正在处理一个相当大的数组，但你可能想尝试一下：

Well, there are a few alternatives. I'm not sure which is the fastest since you're dealing with a sizable array, but you may want to try them out:

您可以使用 随机 ，这将随机整个数组。这可能将有最佳的性能，因为你消耗阵列（10％）的显著部分。

You can use shuffle, which will randomize the entire array. This will likely have the best performance since you're consuming a significant portion of the array (10%).

suffle($seedkeys);
$result = array_slice($seedkeys, 0, 1000);

您可以使用 array_rand （因为你已经说的）在汤姆·黑格指定庄园。这将需要复制的钥匙，所以如果你正在处理的源数组的显著部分，这可能不是最快的。 （注意使用 array_flip 的，它需要允许的使用 array_intersect_key ：

You could use array_rand (as you already said) in the manor that Tom Haigh specifies. This will require copying the keys, so if you're dealing with a significant portion of the source array, this may not be the fastest. (Note the use of array_flip, it's needed to allow the usage of array_intersect_key:

$keys = array_flip(array_rand($seedkeys, 1000));
$result = array_intersect_key($seedkeys, $keys);

如果存储器是紧，最好的解决方案（除了MySQL的一个）将是一个循环，因为它不要求阵列在所有被复制。请注意，这会慢一些，但是如果数组包含了大量的信息，它可能会通过更高效的内存（因为它只会复制正是它返回）...

If memory is tight, the best solution (besides the MySQL one) would be a loop since it doesn't require arrays to be copied at all. Note that this will be slower, but if the array contains a lot of information, it may offset the slowness by being more memory efficient (since it only ever copies exactly what it returns)...

$result = array();
for ($i = 0; $i < 1000; $i++) {
    $result[] = $seedkeys[array_rand($seedkeys)];
}

您可以做到这一点在MySQL中（假设为阵列中的数据从MySQL开始）。要知道，这是简单的，但不是有效的（见月Kneschke的帖子）...

You could do it in MySQL (assuming that the data for the array starts from MySQL). Be aware this is simple, but not that efficient (See Jan Kneschke's post)...

SELECT * FROM `foo` ORDER BY RAND() LIMIT 1000;

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