docs: def select_dataset(self, elangle, quantity):
          """
          Selects the matching dataset and returns its path.
          
          Parameters
          ----------
          elangle : str
              Upper case ascii letter defining the elevation angle
          quantity : str
              Name of the quantity e.g. DBZH, VRAD, RHOHV...
              
          Returns
          -------
          dataset : str
              Path of the matching dataset or None if no dataset is found.
              
          Examples
          --------
          Get the hdf5 path of the DBZH dataset at lowest elevation angle
          
          >>> pvol = odimPVOL('pvol.h5')
          >>> dataset = pvol.select_dataset('A', 'DBZH')
          >>> print(dataset)
          '/dataset1/data1/data'
  
          """
          elangle_path = None
          try:
              search_results = self.search('elangle', self.elangles[elangle])
          except KeyError:
              return None
  
          if search_results == []:
              print('Elevation angle {} is not found from file'.format(elangle))
              print('File contains elevation angles:{}'.format(self.elangles))
          else:
              elangle_path = search_results[0]
                      
          if elangle_path is not None:
              dataset_root = re.search( '^/dataset[0-9]+/', elangle_path).group(0) 
              quantity_path = None
              search_results = self.search('quantity', quantity)
  
              for path in search_results:
                  if dataset_root in path:
                      quantity_path = path
                      break
                      
              if quantity_path is not None:
                  dataset_path = re.search('^/dataset[0-9]+/data[0-9]/', quantity_path).group(0)            
                  dataset_path = os.path.join(dataset_path, 'data')
                  if isinstance(self[dataset_path], h5py.Dataset):
                      self.dataset = self[dataset_path].ref
                      return dataset_path