PHP in_array or array_unique?

What would be the best solution here? If there are less then a 100 items in $list? And what if there are more then a million?

Example 1:

<?php
 foreach($list as $item) {
   if(!in_array($item, $array)){
    $array[] = $item;
   }
 }

 $this->doSomethingWithThisArray($array);
?>

Example 2:

 <?php
  foreach($list as $item) {
   $array[] = $item;
  }

  $this->doSomethingWithThisArray(array_unique($array));
 ?>