Thaylin… that's me!

private function makeRegionList(myMapItemsArr:Array = null):Array {
   var tempArr:Array = myMapItemsArr;
   var keys:Object = {};
   var tempArr2:Array = tempArr.filter(function(item:Object, idx:uint, arr:Array):Boolean {
                        if (keys.hasOwnProperty(item.regionCode)) {
                                        /* If the keys Object already has this property, return false and discard this item. */
                                        return false;
                                    } else {
                                        /* Else the keys Object does *NOT* already have this key, so add this item to the new data provider. */
                                        keys[item.regionCode] = item;
                                        return true;
 
                                    }
                        })
    return tempArr2
}