<?php
$array = array(
'Element1',
'Element2',
'Element3',
'Element1',
'Element1',
'Element4',
'Element4',
'Element2',
'Element2',
'Element2',
'Element2',
'Element4',
'Element5',
'Element5' );
$numbers = array_count_values($array);
asort($numbers);
$result = array_keys($numbers);
print_r($result);
?>