code: def min(self, key=None):
          
  
          def _min(result, item):
              val = data_get(item, key)
  
              if result is None or val < result:
                  return value
  
              return result
  
          return self.reduce(_min)
docs: Get the min value of a given key.
  
          :param key: The key
          :type key: str or None
  
          :rtype: mixed