Unique records with foreach

[Suchy]

foreach($stuff as $x)
    echo $x['letters'] . ",";

 

This prints out something like:

a,d,f,a,e,f,a,a,a,f,v,m,

 

How can I print only unique entries?

a,d,f,e,v,m,

[Barand]

<?php
$letters = array();
foreach($stuff as $x)
    $results[] = $x['letters'];
echo join(',', array_unique($results));