code: def return_rri(self, begsam, endsam):
          
          interval = endsam - begsam
          dat = empty(interval)
          k = 0
              
          with open(self.filename, 'rt') as f:
              [next(f) for x in range(12)]
              
              for j, datum in enumerate(f):
                  
                  if begsam <= j < endsam:
                      dat[k] = float64(datum[:datum.index('\t')])
                      k += 1
                      if k == interval:
                          break
                      
          return dat
docs: Return raw, irregularly-timed RRI.