code: def load_seit_data(directory, frequency_file='frequencies.dat',
                     data_prefix='volt_', **kwargs):
      
      frequencies = np.loadtxt(directory + os.sep + frequency_file)
      data_files = sorted(glob(directory + os.sep + data_prefix + '*'))
      # check that the number of frequencies matches the number of data files
      if frequencies.size != len(data_files):
          raise Exception(
              'number of frequencies does not match number of data files')
  
      # load data
      data_list = []
      for frequency, filename in zip(frequencies, data_files):
          subdata = load_mod_file(filename)
          subdata['frequency'] = frequency
          data_list.append(subdata)
      df = pd.concat(data_list)
      return df, None, None
docs: Load sEIT data from data directory. This function loads data previously
      exported from reda using reda.exporters.crtomo.write_files_to_directory
  
      Parameters
      ----------
      directory : string
          input directory
      frequency_file : string, optional
          file (located in directory) that contains the frequencies
      data_prefix: string, optional
          for each frequency a corresponding data file must be present in the
          input directory. Frequencies and files are matched by sorting the
          frequencies AND the filenames, retrieved using glob and the
          data_prefix
  
      Returns
      -------
      df : pandas.DataFrame
          A DataFrame suitable for the sEIT container
      electrodes : None
          No electrode data is imported
      topography : None
          No topography data is imported