Question

I asked a question almost identical to this a few days ago via this thread and got awesome replies – The biggest lesson for me (aside from the answer itself) was to create a custom object for my holding data.
So, having now done that, can I ask you experts to please show me the most efficient Linq statement to satisfy my requirements?

My Scenario is as follows:

Suppose I have the following holding class:

Public Class Class_Info
    Public Property Teacher As String
    Public Property Name As String
    Public Property Sex As String
End Class

Then, suppose I have the following in another module:

Dim X as new list(of Class_Info)

With the following elements in the list:

Element.Teacher:     Element.Sex:        Element.Name:
Teacher 1            Male                Whatever Name 1
Teacher 2            Female              Whatever Name 2 
Teacher 1            Female              Whatever Name 3
Teacher 1            Female              Whatever Name 4
Teacher 2            Male                Whatever Name 5
Teacher 3            Male                Whatever Name 6
Teacher 3            Female              Whatever Name 7
Teacher 1            Male                Whatever Name 8
Teacher 1            Female              Whatever Name 9
Teacher 2            Male                Whatever Name 10

Now, suppose I want to create the following structure with the following values:

Dim dictTeacherSexName as New Dictionary(Of String, Dictionary(Of String, List(of String)))

Dict1_Key:        Dict1_Value / Dict2_Key:         Dict2_Value:
Teacher 1         Male                             Whatever Name 1
                                                   Whatever Name 8
                  Female                           Whatever Name 3
                                                   Whatever Name 4
                                                   Whatever Name 9
Teacher 2 ...

How could I create that via Linq in the most efficient way?

Thanks!!!

Answer 1

It is the same as last time, however instead of relying on indexes you can point at your object directly.

var result = X.GroupBy(i => i.Teacher)
     .ToDictionary(g => g.Key, g => g
         .GroupBy(i => i.Sex)
         .ToDictionary(h => h.Key, h => h
             .Select(i => i.Name)
             .ToList()));

---

You can also do this with a ILookup for cleaner use. You can use a custom class as your lookup object but it will need to implement IComparable.

class Program
{
    public static void Main()
    {
        var X = new List<Class_Info>();

        X.Add(new Class_Info { Teacher = "Teacher 1", Sex = "Male", Name = "Whatever Name 1" });
        X.Add(new Class_Info { Teacher = "Teacher 2", Sex = "Female", Name = "Whatever Name 2" });
        X.Add(new Class_Info { Teacher = "Teacher 1", Sex = "Female", Name = "Whatever Name 3" });
        X.Add(new Class_Info { Teacher = "Teacher 1", Sex = "Female", Name = "Whatever Name 4" });
        X.Add(new Class_Info { Teacher = "Teacher 2", Sex = "Male", Name = "Whatever Name 5" });
        X.Add(new Class_Info { Teacher = "Teacher 3", Sex = "Male", Name = "Whatever Name 6" });
        X.Add(new Class_Info { Teacher = "Teacher 3", Sex = "Female", Name = "Whatever Name 7" });
        X.Add(new Class_Info { Teacher = "Teacher 1", Sex = "Male", Name = "Whatever Name 8" });
        X.Add(new Class_Info { Teacher = "Teacher 1", Sex = "Female", Name = "Whatever Name 9" });
        X.Add(new Class_Info { Teacher = "Teacher 3", Sex = "Male", Name = "Whatever Name 10" });

        var result = X.ToLookup(key => new Tuple<string,string>(key.Teacher, key.Sex), value => value.Name);

        // Name is a IEnumerable<string> of all names who have "Teacher 1" and are Male.
        var name = result[new Tuple<string,string("Teacher 1","Male")];
    }

    public class Class_Info
    {
        public string Teacher;
        public string Name;
        public string Sex;
    }
}