'Aux method.'

def _sources_as_epochs(self, epochs, add_channels, concatenate):

    out = epochs.copy()
    sources = self._transform_epochs(epochs, concatenate)
    if (add_channels is not None):
        picks = [epochs.ch_names.index(k) for k in add_channels]
    else:
        picks = []
    out._data = (np.concatenate([sources, epochs.get_data()[:, picks]], axis=1) if (len(picks) > 0) else sources)
    self._export_info(out.info, epochs, add_channels)
    out.preload = True
    out._raw = None
    out._projector = None
    return out
