array_unique for arrays inside array

I need a function like array_unique for arrays inside array.

The Case - should be equal, but output "not equal":

<?php
$arr=array(array('a',1),array('a',2));
$arr2=array_unique($arr);
if($arr2==$arr){
  echo "equal";
}
else{
  echo "not equal";
}
?>

How should the code be changed to get output "equal"?