@staticmethod
def _prior_timepoint_generator(ts_group, cond):
    """
        Yield the previous timepoint condition name and delt until it gets back to the first timepoint
        :param cond:
        """
    prev_cond, prev_delt = ts_group[cond][0]
    while prev_cond is not None:
        yield prev_cond, prev_delt
        prev_cond, prev_delt = ts_group[prev_cond][0]
