If you have an array like:
array(
array('key' => 'value'),
array('key' => 'anotherValue'),
array('key' => 'sameValue'),
array('key' => 'sameValue')
);
and you want to make sure that you cant have 'key' with same value twice
i was searching a native way to do it, but couldn't find one - so this is my solution: