def METHOD_NAME(f_obs, params):
  if (f_obs.is_xray_intensity_array()):
    f_obs = f_obs.f_sq_as_f()
  f_obs = f_obs.map_to_asu()
  if (not f_obs.is_unique_set_under_symmetry()):
    f_obs = f_obs.merge_equivalents().array()
  if (f_obs.sigmas() is not None):
    f_obs = f_obs.select(f_obs.sigmas() > 0)
    f_obs = f_obs.select((f_obs.data() / f_obs.sigmas()) > params.min_sigma_ratio)
  return f_obs