http://www.php.net/manual/es/ref.array.php
busca ahi una funcion que se acomode a lo que necesitas, hay muchas.
Ejemplo 1. array_intersect() example
<?php
$array1 = array("a" => "green", "red", "blue");
$array2 = array("b" => "green", "yellow", "red");
$result = array_intersect($array1, $array2);
?>
This makes $result have
Array
(
[a] => green
[0] => red
)