<%= f.select :gender, options_for_select(['Male', 'Female']), { prompt: '--select gender--', selected: params[profile: [:gender]] }, { class: 'form-control' } %>

def user_params
      params.require(:user).permit(
        :email, :password, :password_confirmation,
        profile_attributes: [
            :user_id, :first_name, :last_name, :gender, :date_of_birth,
            :occupation, :education, :city, :post_code, :country
        ]
      )
end