protected function buildSortedMap(array $definition) {
		$sortArgs = [];
		
		foreach ($definition as $definitionPart) {
			list($property, $direction) = $this->parseSortDefinition($definitionPart);
			
			$sortArgs[] = $this->getDataColumn($property);
			$sortArgs[] = $direction;
		}
		
		$this->_map = array_keys($this->_data);
		$sortArgs[] = &$this->_map;
		
		call_user_func_array('array_multisort', $sortArgs);
	}