docs: def sort_amounts(proteins, sort_index):
      """Generic function for sorting peptides and psms. Assumes a higher
      number is better for what is passed at sort_index position in protein."""
      amounts = {}
      for protein in proteins:
          amount_x_for_protein = protein[sort_index]
          try:
              amounts[amount_x_for_protein].append(protein)
          except KeyError:
              amounts[amount_x_for_protein] = [protein]
      return [v for k, v in sorted(amounts.items(), reverse=True)]