array_unique & multi-dimensional arrays

I am trying to clean up some junky code in a journal/news type script and redoing the archive navigation. I am pulling all of the dates of the entries and pushing it into a multi- dimensional array like so: array_push($archive_nav, array(month => $month, year => $year, longmonth => $longmonth)); I assumed I could just use array_unique to filter out all of the duplicates in the array. But it doesn't seem to work that way, and the only month/year combo I end up with is the very oldest one (according to year/month) in the array. $archive_nav = array_unique($archive_nav); If I leave out array_unique, I am getting all of the appropriate month/year combos in my script while doing a foreach... just one for every single entry in the database for that combo (which is a lot in some cases!). Is there a better way to do this? sasha