in_array vs isset-性能 [英] in_array vs isset - performance

问题描述

请考虑以下代码段:

示例1

$array = Array(1,2,3,4,5,6,7);
$array_test = Array(3,5,4,7,3,6,7,8,8,9,3);

foreach($array_test as $value) {
   if(in_array($value, $array)) {
       // do some magic here
   }
}

示例2

$array = Array(1,2,3,4,5,6,7);
$array_test = Array(3,5,4,7,3,6,7,8,8,9,3);

$array_index = Array();
foreach($array as $value) {
    $array_index[ $value ] = true;
}

foreach($array_test as $value) {
   if(isset($array_index[ $value ])) {
       // do some magic here
   }
}

很明显，两个片段都执行相同的工作.在某些阵列样本中，示例1比示例2更快.

Obviously both snippets do the same jobs. In some array samples example #1 is faster than example #2.

我确定我们都处于这两种情况下，但是我的问题是:

I am sure we all were in both situations, however my question is:

• 我应该总是选择#2吗?
• 我何时应该选择#1?当 $ array * $ array_test 的大小为<时，10个?< 100?< 1000?
• 如何确定在特定情况下哪种方法更好?
• 也许除了使用临时表 $ array_index 之外，还有其他技巧.我不记得其他编程语言中的类似情况，一切准备就绪

• Should I always choose #2?
• When should I choose #1? When size of $array * $array_test is < 10? <100? <1000?
• How to determine which method is better in particular situation?
• Maybe there is some other trick than using temp table $array_index. I don't remember similar situation in other programming languages, everything was ready as-you-go

也请注意关联键.

有人已经问过非常类似的问题:

Someone already asked very similar question:

• 更快的是什么:in_array或isset?

推荐答案

在第二个示例中，必须先构造 $ array 的翻转"值，然后才能使用 isset().顺便说一句，您也可以使用 array_flip() .

In your second example, you have to construct the "flipped" value of $array before you can use isset(). Btw, you can also use array_flip() for that.

如果您可以立即使用数组键(无需转换)，请使用 isset()，因为由于查找键的方式，它显然比 in_array()快得多和，因为它是一种语言构造.

If you can use array keys immediately (without conversion), use isset() because it's obviously much faster than in_array() due to way keys are looked up and because it's a language construct.

如果不进行转换就无法使用键，则可以考虑将 in_array()用于小型数组.对于更大的阵列，可能值得运行基准测试来确定是否仍然值得进行阵列转换.

If you can't use the keys without conversion, you could consider using in_array() for small arrays. For bigger arrays it might be worthwhile to run a benchmark to determine whether an array conversion step would still be worth it.

最后，并且在很大程度上取决于情况，您也可以使用 array_intersect _ 函数之一，主要是为了避免在PHP代码内部循环.

Lastly, and depending largely on the situation, you could use one of the array_intersect_ functions as well, mainly to avoid having to loop inside PHP code.

这篇关于in_array vs isset-性能的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！