Very useful function i have using: joinr (join-recursive).
It allows you easy join of multi-level arrays.
For example, if you have
  $intervals = array(array(5, 9), array(11, 15), array(22, 24))
and want to have comma-separated list of dash-separated intervals, just do
  print joinr(array(",","-"), $intervals);
Here is function code:
<?php
    function joinr($join, $value, $lvl=0)
    {
        if (!is_array($join)) return joinr(array($join), $value, $lvl);
        $res = array();
        if (is_array($value)&&sizeof($value)&&is_array(current($value))) { // Is value are array of sub-arrays?
            foreach($value as $val)
                $res[] = joinr($join, $val, $lvl+1);
        }
        elseif(is_array($value)) {
            $res = $value;
        }
        else $res[] = $value;
        return join(isset($join[$lvl])?$join[$lvl]:"", $res);
    }
?>
<?php
$array = array('lastname', 'email', 'phone');
$comma_separated = join(",", $array);
echo $comma_separated; // lastname,email,phone
?>