def _format_data(self, data):
        """
        Sort the data in blue wavelengths to red, and ignore any spectra that
        have entirely non-finite or negative fluxes.
        """
        return [spectrum for spectrum in \
            sorted(data if isinstance(data, (list, tuple)) else [data],
                key=lambda x: x.disp[0]) if np.any(np.isfinite(spectrum.flux))]