Find last known allergies for each patient

Question:
How can we use HL7Spy to find the last set of known allergies for each patient in a set of messages?

Answer:
The best way is to write a custom function that remembers the last set of allergies for each patient. Then in the OnFinished function we print out all patients with their last set of known allergies.

string _fileName = @"c:\temp\_test.txt";
Dictionary<string,Patient> _data = new Dictionary<string,Patient>(10000);

public class Patient
{
   public Patient(string patientId) 
   { 
    Allergies = new HashSet<string>();
    PatientId = patientId;
   }
   public HashSet<string> Allergies;
   public string PatientId;
}

public override void Run() { 
  // Get an HL7 Message in parsed format
  HL7Message message = GetParsedMessage();
  MSH msh = message.Segments.First<MSH>();
  if(msh==null || msh.MessageType_09.TriggerEvent_02.Value!="A08")
    return; // not an ADT^A08 message
  
  PID pid = message.Segments.First<PID>();
  if(pid==null)
    return; // no pid segment
  
  List<AL1> patientAllergies = message.Segments.OfType<AL1>();
  if(patientAllergies.Count==0)
    return; // no allergies
  
  string patientId = pid.PatientIdentifierList_03.First.ToString();  
  
  Patient pat;
  if(!_data.TryGetValue(patientId,out pat))
  {
     pat = new Patient(patientId); 
     _data.Add(patientId,pat);
  }
  
  pat.Allergies.Clear();
  
  // loop through all AL1 segments
  foreach(AL1 al1 in patientAllergies)
  {
     pat.Allergies.Add(al1.AllergenTypeCode_02.ToString());
   }
}
// Called once after the last message has been processed.
// It is a good place to perform cleanup and to report information.
// Always called from the UI thread.
public override void OnFinish() 
{
  // to figure out the distribution of all allergies
  Dictionary<string, int> allergies = new Dictionary<string,int>(1000);
  
  // write the data out to a file
  using(System.IO.StreamWriter wr = new System.IO.StreamWriter(_fileName))
  {   
    wr.WriteLine("Patient ID vs Allergy for {0} patient samples",_data.Count);
    wr.WriteLine();
   
    foreach(Patient p in _data.Values.OrderByDescending(p=>p.Allergies.Count))
    {
        wr.Write(p.PatientId);
        wr.Write(',');
        wr.Write(p.Allergies.Count); 
        foreach(string s in p.Allergies)
        {
           wr.Write(',');
           wr.Write(s);         
           // calculate the total number of allergy types for the given set of patients
           int frequency=0;
           if(!allergies.TryGetValue(s,out frequency))
           {
              allergies.Add(s,1);
           } else {
              allergies[s]=++frequency;
           }
        }
        wr.WriteLine();
    }
    
    wr.WriteLine();
    wr.WriteLine();
    wr.WriteLine("Allergy distribution for {0} patient samples.",_data.Count);
    wr.WriteLine("Number of distinct allergies is {0}.",allergies.Count);    
    wr.WriteLine();
    
    foreach(KeyValuePair<string,int> d in allergies)
    {
      wr.Write(d.Key);
      wr.Write(',');
      wr.Write(d.Value);
      wr.WriteLine();
    }       
  }
// launch notepad to display the file.
System.Diagnostics.Process.Start("Notepad",_fileName);
 }