ValueError("The least populated class in y has only 1"
                         " member, which is too few. The minimum"
                         " number of groups for any class cannot"
                         " be less than 2.")

if np.min(class_counts) < 2:
        raise ValueError("The least populated class in y has only 1"
                         " member, which is too few. The minimum"
                         " number of groups for any class cannot"
                         " be less than 2.")