How to use the @requestnetwork/utils.flatten2DimensionsArray function in @requestnetwork/utils

public async getChannelIdsFromMultipleTopics(topics: string[]): Promise {
    const channelIdsPromises = topics.map(async topic => {
      return Array.from((await this.channelIdByTopics.get(topic)) || []);
    });
    const channelIds = await Promise.all(channelIdsPromises);

    // flatten the array of array and remove the duplicates
    return Utils.unique(Utils.flatten2DimensionsArray(channelIds)).uniqueItems;
  }
  /**

          .then(halves => Utils.flatten2DimensionsArray(halves))
          .catch(err => {