If you have an array with duplicate values, sometimes you might need to show only non-unique elements. Here is a short code in PHP that will allow you to do this.
<?
$arr=array_map("trim", file("file.txt"));
$nonuniq=array_unique(array_diff_assoc($arr, array_unique($arr)));
?>
This will return unique array of duplicates. If you need to show all duplicated values, use this code.
<?
$arr=array_map("trim", file("file.txt"));
$nonuniq=array_diff_assoc($arr, array_unique($arr));
?>
