public function chunk($size, $offset = 0) {
		$data      = $this->createClone();
		$availSize = count($this->_map) - $offset;
		
		if ($size > $availSize) {
			$size = $availSize;
		}
		
		$last = $size + $offset;
		
		for ($i = $offset; $i < $last; ++$i) {
			$key = $this->_map[$i];
			
			if (isset($this->_models[$key])) {
				$data->setItem($key, $this->_models[$key]);
			} else {
				$data->setItem($key, $this->_data[$key]);
			}
		}
		
		return $data;
	}