docs: def create_index_tuple(group_ids):
      """An helper function to create index tuples for fast lookup in HDF5Pump"""
      max_group_id = np.max(group_ids)
  
      start_idx_arr = np.full(max_group_id + 1, 0)
      n_items_arr = np.full(max_group_id + 1, 0)
  
      current_group_id = group_ids[0]
      current_idx = 0
      item_count = 0
  
      for group_id in group_ids:
          if group_id != current_group_id:
              start_idx_arr[current_group_id] = current_idx
              n_items_arr[current_group_id] = item_count
              current_idx += item_count
              item_count = 0
              current_group_id = group_id
          item_count += 1
      else:
          start_idx_arr[current_group_id] = current_idx
          n_items_arr[current_group_id] = item_count
  
      return (start_idx_arr, n_items_arr)