array_diff 如何工作? [英] How does array_diff work?

问题描述

array_diff() 如何工作?它显然不能如下工作:

How does array_diff() work? It obviously couldn't work as follows:

function array_diff($arraya, $arrayb)
{
    $diffs = array();
    foreach ($arraya as $keya => $valuea)
    {
        $equaltag = 0;
        foreach ($arrayb as $valueb)     
        {
            if ($valuea == $valueb)
            {
                $equaltag =1;
                break;
            }
        }
        if ($equaltag == o)
        {
              $diffs[$keya]=$valuea;
        }

    }
    return $diffs;                          
}                                  //couldn't be worse than this

有人知道更好的解决方案吗?

Does anyone know a better solution?

编辑@animuson:

EDIT @animuson:

function array_diff($arraya, $arrayb)
{
    foreach ($arraya as $keya => $valuea)
    {
        if (in_array($valuea, $arrayb))
        {
            unset($arraya[$keya]);
        }
    }
    return $arraya;
}

推荐答案

UPDATE

• 参见下文以获取更快/更好的代码.

• see below for faster/better code.

array_diff 在 php 5.3.4 中的表现要好得多，但仍然比 Leo 的函数慢约 10 倍.

array_diff behaviour is much better in php 5.3.4, but still ~10 times slower than Leo's function.

另外值得注意的是，这些函数并不严格等同于 array_diff，因为它们不维护数组键，即 my_array_diff(x,y) == array_values(array_diff(x,y)).

also it's worth noting that these functions are not strictly equivalent to array_diff since they don't maintain array keys, i.e. my_array_diff(x,y) == array_values(array_diff(x,y)).

/更新

更好的解决方案是使用哈希映射

function my_array_diff($a, $b) {
    $map = $out = array();
    foreach($a as $val) $map[$val] = 1;
    foreach($b as $val) if(isset($map[$val])) $map[$val] = 0;
    foreach($map as $val => $ok) if($ok) $out[] = $val;
    return $out;
}

$a = array('A', 'B', 'C', 'D');
$b = array('X', 'C', 'A', 'Y');

print_r(my_array_diff($a, $b)); // B, D

基准

function your_array_diff($arraya, $arrayb)
{
    foreach ($arraya as $keya => $valuea)
    {
        if (in_array($valuea, $arrayb))
        {
            unset($arraya[$keya]);
        }
    }
    return $arraya;
}

$a = range(1, 10000);
$b = range(5000, 15000);

shuffle($a);
shuffle($b);

$ts = microtime(true);
my_array_diff($a, $b);
printf("ME =%.4f\n", microtime(true) - $ts);

$ts = microtime(true);
your_array_diff($a, $b);
printf("YOU=%.4f\n", microtime(true) - $ts);

结果

ME =0.0137
YOU=3.6282

有什么问题吗?;)

而且，只是为了好玩，

$ts = microtime(true);
array_diff($a, $b);
printf("PHP=%.4f\n", microtime(true) - $ts);

结果

ME =0.0140
YOU=3.6706
PHP=19.5980

太不可思议了！

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