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<?php $array = array( 3 => 2, 2 => 1, 1 => NULL, 4 => NULL, ); uasort($array, function ($a, $b) { if ($a === $b) { return 0; } elseif ($a === NULL) { return 1; } elseif ($b === NULL) { return -1; } return ($a < $b) ? -1 : 1; }); var_dump($array);

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61.08 ms | 402 KiB | 5 Q