'Returns
self
Removes a particular preference for a user.'

def remove_preference(self, user_id, item_id):

    user_id_loc = np.where((self._user_ids == user_id))
    item_id_loc = np.where((self._item_ids == item_id))
    if (not user_id_loc[0].size):
        raise UserNotFoundError('user_id    in    the    model    not    found')
    if (not item_id_loc[0].size):
        raise ItemNotFoundError('item_id    in    the    model    not    found')
    self.dataset[user_id].remove(item_id)
    self.build_model()
