gistfile1.txt

NSMutableArray *CustomClassArray = //Objects of type array


class CustomClass : Object 
{
  @property NSString *objectID;
}

NSMutableArray *filteredArray = [NSMutableArray new];

for (CustomClass *customClass in CustomClassArray) {
    [filteredArray addObject:.... ?] //Only if filteredArray not contains another customClass object with the same objectID
}