Удаление дубликатов в конце функции

tuple<vector<string>, DocumentStatus> SearchServer::MatchDocument(execution::parallel_policy policy,
    const string& raw_query, int document_id) const {
    if (!IsValidWord(raw_query)) {
        throw invalid_argument("Некорректный поисковый запрос.");
    }
    if (document_id < 0) {
        throw out_of_range("Документа с указанным id не существует.");
    }
    Query query = ParseQuery(raw_query);
    vector<string> matched_words(query.plus_words.size());

    vector<string>::iterator end_new_size = copy_if(policy, query.plus_words.begin(), query.plus_words.end(),
        matched_words.begin(),
        [this, document_id](const string& plus_word) {
            return word_frequencies_in_document_.at(document_id).count(plus_word);
        });
    matched_words.resize(distance(matched_words.begin(), end_new_size));

    if (find_if(policy, query.minus_words.begin(), query.minus_words.end(),
        [this, document_id](const string& minus_word) {
            return word_frequencies_in_document_.at(document_id).count(minus_word);
        }) != query.minus_words.end()) {
        matched_words.clear();
    }

    if (!matched_words.empty()) {
        sort(policy, matched_words.begin(), matched_words.end());
        vector<string>::iterator last = unique(policy, matched_words.begin(), matched_words.end());
        matched_words.erase(last, matched_words.end());
    }

    return { matched_words, documents_.at(document_id).status };
}