code: def network_sampling(n, filename, directory=None, snowball=False, user=None):
      if snowball:
          if user is None:
              raise ValueError("Must specify a starting user from whom to initiate the snowball")
          else:
              users, agenda = [user], [user]
              while len(agenda) > 0:
                  parent = agenda.pop()
                  dealphebetized_network = sorted(parent.network.items(), key=lambda k: random.random())
                  for neighbor in dealphebetized_network:
                      if neighbor[1] not in users and neighbor[1] is not None and len(users) < n:
                          users.append(neighbor[1])
                          if neighbor[1].network:
                              agenda.push(neighbor[1])
      else:
          files = [x for x in os.listdir(directory) if os.path.isfile(os.path.join(directory, x))]
          shuffled_files = sorted(files, key=lambda k: random.random())
          user_names = shuffled_files[:n]
          users = [bc.read_csv(u[:-4], directory) for u in user_names]
      if len(users) < n:
          raise ValueError("Specified more users than records that exist, only {} records available".format(len(users)))
      bc.to_csv([bc.utils.all(u) for u in users], filename)