Convert list field to CSV string

<?php
// Help Scout 24815
// process list field 9 (only) into a CSV string to pass to Sugar CRM
// initialize an empty string to hold field 9 array items
$field_9_as_csv = '';
// you have to use a Gravity Forms hook which passes in the $entry to use this code
foreach ($entry as $key => $value) {
        // the $entry array key begins with a 9, our list field
        if (substr($key, 0, 1) == '9') {
                // if there is a $value for this array key, i.e. not empty
                if (strlen($value) > 0) {
                        $field_9_as_csv = $field_9_as_csv . $value . ', ';
                }
        }
}
// strip final trailing comma and one space (two characters)
$field_9_as_csv = substr($field_9_as_csv, 0, -2);
// send $field_9_as_csv to Sugar CRM