docs: def _get_sample_select(samples, keep):
      """Returns a vector of True/False to keep samples."""
      k = np.ones_like(samples, dtype=bool)
      if keep is not None:
          k = np.array([s in keep for s in samples], dtype=bool)
          if np.sum(k) == 0:
              logger.warning("No samples matched the keep list")
      return k