def merge_idxs(self, idxs):
        if len(idxs) == 0:
            return self.make_idx_array(0, 0)

        return numpy.concatenate(idxs)
Return source and target index arrays, built up from
dataset/ETHPy150Open OpenMDAO/OpenMDAO/openmdao/core/vec_wrapper.py/VecWrapper.merge_idxs