Merge pull request #1949 from peastman/ids

      self._cache_used += shard_size

    return (shard.X, shard.y, shard.w, shard.ids)

  def get_shard_ids(self, i):

    """Retrieves the list of IDs for the i-th shard from disk."""

    if self._cached_shards is not None and self._cached_shards[i] is not None:

      return self._cached_shards[i].ids

    row = self.metadata_df.iloc[i]

    return np.array(

        load_from_disk(os.path.join(self.data_dir, row['ids'])), dtype=object)

  def add_shard(self, X, y, w, ids):

    """Adds a data shard."""

    metadata_rows = self.metadata_df.values.tolist()

    if len(self) == 0:

      return np.array([])

    ids = []

    for (_, _, _, ids_b) in self.itershards():

      ids.append(np.atleast_1d(np.squeeze(ids_b)))

    for i in range(self.get_number_shards()):

      ids.append(np.atleast_1d(np.squeeze(self.get_shard_ids(i))))

    return np.concatenate(ids)

  @property