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12 years ago
I bench-marked some uses of array_intersect and can't believe how slow it is. This isn't as elaborate, but handles most cases and is much faster:

<?php
/**
examines two arrays and returns the intersected arrays with matching keys (ignores duplicate keys)
*/
function simple_array_intersect($a,$b) {
    $a_assoc = $a != array_values($a);
    $b_assoc = $b != array_values($b);
    $ak = $a_assoc ? array_keys($a) : $a;
    $bk = $b_assoc ? array_keys($b) : $b;
    $out = array();
    for ($i=0;$i<sizeof($ak);$i++) { 
        if (in_array($ak[$i],$bk)) {
            if ($a_assoc) {
                $out[$ak[$i]] = $a[$ak[$i]];
            } else {
                $out[] = $ak[$i];
            }
        }
    }
    return $out;
}

?>

You can try this out with this:

<?php
// create a large array (simple)
$first = array();
for ($i=500;$i<500000;$i++) {
    $first[] = $i;
}
// create a smaller array (associative)
$second = array();
for ($i=499990;$i<500000;$i++) {
    $second[$i] = rand();
}
echo microtime(true)."\n";
// built-in function
print_r(array_intersect($first,$second));
echo microtime(true)."\n";
// favour simple array as match
print_r(simple_array_intersect($first,$second));
echo microtime(true)."\n";
// favour associative keys for match
print_r(simple_array_intersect($second,$first));
echo microtime(true)."\n";

?>
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