code: def save_block_to_crt(filename, group, norrec='all', store_errors=False):
      
      if norrec != 'all':
          group = group.query('norrec == "{0}"'.format(norrec))
  
      # todo: we need to fix the global naming scheme for columns!
      with open(filename, 'wb') as fid:
          fid.write(
              bytes('{0}\n'.format(len(group)), 'UTF-8')
          )
  
          AB = group['a'] * 1e4 + group['b']
          MN = group['m'] * 1e4 + group['n']
          line = [
              AB.values.astype(int),
              MN.values.astype(int),
              group['r'].values,
          ]
  
          if 'rpha' in group:
              line.append(group['rpha'].values)
          else:
              line.append(group['r'].values * 0.0)
  
          fmt = '%i %i %f %f'
          if store_errors:
              line += (
                  group['d|Z|_[Ohm]'].values,
                  group['dphi_[mrad]'].values,
              )
              fmt += ' %f %f'
  
          subdata = np.array(line).T
          np.savetxt(fid, subdata, fmt=fmt)
docs: Save a dataset to a CRTomo-compatible .crt file
  
      Parameters
      ----------
      filename : string
          Output filename
      group : pandas.group
          Data group
      norrec : string
          Which data to export Possible values: all|nor|rec
      store_errors : bool
          If true, store errors of the data in a separate column