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copied!<p>UPDATE </p> <ul> <li><p><a href="https://stackoverflow.com/questions/2479963/how-does-array-diff-work/6700430#6700430">see below</a> for faster/better code. </p></li> <li><p>array_diff behaviour is much better in php 5.3.4, but still ~10 times slower than Leo's function.</p></li> <li><p>also it's worth noting that these functions are not strictly equivalent to <code>array_diff</code> since they don't maintain array keys, i.e. <code>my_array_diff(x,y) == array_values(array_diff(x,y))</code>. </p></li> </ul> <p>/UPDATE</p> <p>A better solution is to use <a href="http://en.wikipedia.org/wiki/Hash_table" rel="nofollow noreferrer">hash maps</a></p> <pre><code>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, $b)); // B, D </code></pre> <p>benchmark</p> <pre><code>function your_array_diff($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) - $ts); </code></pre> <p>result</p> <pre><code>ME =0.0137 YOU=3.6282 </code></pre> <p>any questions? ;)</p> <p>and, just for fun,</p> <pre><code>$ts = microtime(true); array_diff($a, $b); printf("PHP=%.4f\n", microtime(true) - $ts); </code></pre> <p>result</p> <pre><code>ME =0.0140 YOU=3.6706 PHP=19.5980 </code></pre> <p>that's incredible!</p>

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