/// <summary>
/// Returns the string that MSstats code uses to identify a row of data in the MSstats Input report.
/// </summary>
private static string GetFeatureKey(SrmDocument document, IdentityPath identityPath)
{
PeptideGroupDocNode peptideGroup = (PeptideGroupDocNode)document.FindNode(identityPath.GetIdentity(0));
PeptideDocNode peptide = (PeptideDocNode)peptideGroup.FindNode(identityPath.GetIdentity(1));
TransitionGroupDocNode transitionGroup =
(TransitionGroupDocNode)peptide.FindNode(identityPath.GetIdentity(2));
TransitionDocNode transition = (TransitionDocNode)transitionGroup.FindNode(identityPath.GetIdentity(3));
return(peptide.ModifiedSequenceDisplay + '_' + transitionGroup.PrecursorCharge + '_' + GetFragmentIon(transition) +
'_' + transition.Transition.Charge);
}