public int compare(Peptide pep1, Peptide pep2) {

    Double pep1Value = pep1.getIonScore();
    Double pep2Value = pep2.getIonScore();

    if (direction == SortingDirection.Ascending) return pep1Value.compareTo(pep2Value);
    else return pep2Value.compareTo(pep1Value);
  }