def biases(self, vector_id=0):
        """
        Return the frame for the respective bias vector.

        :param: vector_id: an integer, ranging from 0 to number of layers, that specifies the bias vector to return.
        :returns: an H2OFrame which represents the bias vector identified by vector_id
        """
        return {model.model_id: model.biases(vector_id) for model in self.models}