Initialize empty vector of vectors with elements of vector of vectors

I have a function which shall initialize an empty vector of vectors from type string with certain elements from an given vector of vectors from type string. My syntax looks like this

std::vector<std::vector<std::string>> extract_data_on_userid(const std::vector<std::vector<std::string>> &array, std::vector<std::string> &user_ids, const int nr_of_events)
{
  std::vector<std::vector<std::string>> data_extract;
  int event_iterator = 0;
  int user_id_iterator = 0;

  // While loops which extracts the events based on user IDs
  while (event_iterator <= nr_of_events)
  {
    // While loop which finds specified user id in an event
    while (user_id_iterator < array[0].size())
    {
      if (check_id(user_ids, array[0][user_id_iterator]))
      {
        for (size_t i = 0; i < array.size(); i++)
        {
          data_extract[i].push_back(array[i][user_id_iterator]);
        }
      }
      user_id_iterator++;
    }

    event_iterator++;
  }

  return data_extract;
}

The given vector consists on varying number of string vectors (at least 2). My method shall search for certain UserIDs in

check_id(user_ids, array[0][user_id_iterator])

an then push the relevant event (user_id_iterator) in a new 2D Vector for all 1D Vectors

vector[i:in][user_id_iterator]

Into the newly initiated vector

std::vector<std::vector<std::string>> data_extract;

over the for loop.

 for (size_t i = 0; i < array.size(); i++)
    {
      data_extract[i].push_back(array[i][user_id_iterator]);
    }

It all does work as expected until the elements of the vectors[i:in] in row [user_id_iterator] shall be pushed into the emtpy vectors.

Do I intially have to initialize all 1D vectors in the 2D Vector data_extract? What is the correct syntax to fill an empty vector of vectors which certain elements from a filled vector of vectors? I receive an exception (segmentation fault) because the emtpy vector is not initialized correctly.