static void Main(string[] args) {
List<InstanceInformation> infos = new List<InstanceInformation>() {
new InstanceInformation(){ SeriesID = "A", StudyID = "A1", PatientID = "P1" },
new InstanceInformation(){ SeriesID = "A", StudyID = "A1", PatientID = "P1" },
new InstanceInformation(){ SeriesID = "A", StudyID = "A1", PatientID = "P2" },
new InstanceInformation(){ SeriesID = "A", StudyID = "A2", PatientID = "P1" },
new InstanceInformation(){ SeriesID = "B", StudyID = "B1", PatientID = "P1"},
new InstanceInformation(){ SeriesID = "B", StudyID = "B1", PatientID = "P1"},
};
IEnumerable<IGrouping<string, InstanceInformation>> bySeries = infos.GroupBy(g => g.SeriesID);
IEnumerable<IGrouping<string, InstanceInformation>> byStudy = bySeries.SelectMany(g => g.GroupBy(g_inner => g_inner.StudyID));
IEnumerable<IGrouping<string, InstanceInformation>> byPatient = byStudy.SelectMany(g => g.GroupBy(g_inner => g_inner.PatientID));
foreach (IGrouping<string, InstanceInformation> group in byPatient) {
Console.WriteLine(group.Key);
foreach(InstanceInformation II in group)
Console.WriteLine(" " + II.ToString());
}
}
