code: def _sum_by_samples(seqs_freq, samples_order):
      
      n = len(seqs_freq[seqs_freq.keys()[0]].freq.keys())
      y = np.array([0] * n)
      for s in seqs_freq:
          x = seqs_freq[s].freq
          exp = [seqs_freq[s].freq[sam] for sam in samples_order]
          y = list(np.array(exp) + y)
      return y
docs: Sum sequences of a metacluster by samples.