'Returns the residuals, the endogeneous data minus the fitted
values from the model.  The residuals are returned as a list
of arrays containing the residuals for each cluster.'

@cache_readonly
def resid_split(self):

    sresid = []
    for v in self.model.group_labels:
        ii = self.model.group_indices[v]
        sresid.append(self.resid[ii])
    return sresid
