<!-- Collection of code snippets by Arne Vajhøj -->
<!-- posted to eksperten.dk, usenet and other places (2002-now) -->
<?php
$a = array('A', 'B', 'C', 'D', 'B', 'C', 'X', 'C');
echo implode(' ', $a) . "\r\n";
$withdupl = array_keys(array_filter(array_count_values($a), function($v) { return$v > 1; }));
echo implode(' ', $withdupl) . "\r\n";
$withoutdupl = array_diff($a, $withdupl);
echo implode(' ', $withoutdupl) . "\r\n";
?>