This method returns the indices of each entity's neighbors. A tensor
        is accepted as a parameter for copying purposes.

        Parameters
        ----------
        worlds : ``List[WikiTablesWorld]``
        num_entities : ``int``
        tensor : ``torch.Tensor``
            Used for copying the constructed list onto the right device.

        Returns
        -------
        A ``torch.LongTensor`` with shape ``(batch_size, num_entities, num_neighbors)``. It is padded
        with -1 instead of 0, since 0 is a valid neighbor index.

def _get_neighbor_indices(worlds: List[WikiTablesWorld],
                              num_entities: int,
                              tensor: torch.Tensor) -> torch.LongTensor:
        """
        This method returns the indices of each entity's neighbors. A tensor
        is accepted as a parameter for copying purposes.

        Parameters
        ----------
        worlds : ``List[WikiTablesWorld]``
        num_entities : ``int``
        tensor : ``torch.Tensor``
            Used for copying the constructed list onto the right device.

        Returns
        -------
        A ``torch.LongTensor`` with shape ``(batch_size, num_entities, num_neighbors)``. It is padded
        with -1 instead of 0, since 0 is a valid neighbor index.
        """

        num_neighbors = 0
        for world in worlds:
            for entity in world.table_graph.entities:
                if len(world.table_graph.neighbors[entity]) > num_neighbors:
                    num_neighbors = len(world.table_graph.neighbors[entity])

        batch_neighbors = []
        for world in worlds:
            # Each batch instance has its own world, which has a corresponding table.
            entities = world.table_graph.entities
            entity2index = {entity: i for i, entity in enumerate(entities)}
            entity2neighbors = world.table_graph.neighbors
            neighbor_indexes = []
            for entity in entities:
                entity_neighbors = [entity2index[n] for n in entity2neighbors[entity]]
                # Pad with -1 instead of 0, since 0 represents a neighbor index.
                padded = pad_sequence_to_length(entity_neighbors, num_neighbors, lambda: -1)
                neighbor_indexes.append(padded)
            neighbor_indexes = pad_sequence_to_length(neighbor_indexes,
                                                      num_entities,
                                                      lambda: [-1] * num_neighbors)
            batch_neighbors.append(neighbor_indexes)
        return tensor.new_tensor(batch_neighbors, dtype=torch.long)