a private method to reset the weight for a list of observation names.  Supports the
        data worth analyses in pyemu.Schur class.  This method only adjusts
        observation weights in the current weight is nonzero.  User beware!
        Parameters
        ----------
        obslist : list
            list of observation names
        weight : (float)
            new weight to assign

def _adjust_weights_by_list(self, obslist, weight):
        """a private method to reset the weight for a list of observation names.  Supports the
        data worth analyses in pyemu.Schur class.  This method only adjusts
        observation weights in the current weight is nonzero.  User beware!
        Parameters
        ----------
        obslist : list
            list of observation names
        weight : (float)
            new weight to assign
        """

        obs = self.observation_data
        if not isinstance(obslist, list):
            obslist = [obslist]
        obslist = set([str(i).lower() for i in obslist])
        # groups = obs.groupby([lambda x:x in obslist,
        #                     obs.weight.apply(lambda x:x==0.0)]).groups
        # if (True,True) in groups:
        #    obs.loc[groups[True,True],"weight"] = weight
        reset_names = obs.loc[obs.apply(lambda x: x.obsnme in obslist and x.weight == 0, axis=1), "obsnme"]
        if len(reset_names) > 0:
            obs.loc[reset_names, "weight"] = weight