[TYPO3-mvc] How to sort objects

[Stefan Kruse]

Hi, i have many company objects which have a 1:1 relation to country and
city. Now I give out a query result with all companies in a for loop. In the
sidemenü I need a menu with all countries and cities from the companies. How
can I now get the individual countries. This should be sorted
alphabetically. And should only be used once. Could  someone give me a hint?
Thanks Stefan