http://stackoverflow.com/q/6238985/

RWServerListController.m

// -setServers:
dictionaryForDuplicateHostnameChecking = [[NSMutableDictionary dictionary] retain]; // release in -dealloc
for (RWServer *server in self.servers) {
  if ([dictionaryForDuplicateHostnameChecking objectForKey:server.hostname]) {
    NSMutableArray *array = [dictionaryForDuplicateHostnameChecking objectForKey:server.hostname];
    [array addObject:server.hostname];
  } else {
    [dictionaryForDuplicateHostnameChecking setObject:[NSMutableArray arrayWithObject:server] forKey:server.hostname];
  }
}

// -tableView:cellForRowAtIndexPath:
RWServer *server = [self.servers objectAtIndex:indexPath.row];
if ([[dictionaryForDuplicateHostnameChecking objectForKey:server.hostname] count] > 1) {
  cell.textLabel.text = [server.hostname stringByAppendingFormat:@":%u", server.port, nil];
} else {
  cell.textLabel.text = server.hostname;
}