Question

Suppose that we have this class:

public enum KindOfPerson
{
    Student, Teacher, ...
}

public class Person
{
    // This contains only numbers between 0 and 1
    public double ScorePercent { get; set; }
    public KindOfPerson Type { get; set; }
}

I’m trying to classify a list by KindOfPerson, but also I’d like to know what is the average of ScorePercent of all the people of the same KindOfPerson.

List<List<Person>> groupedLists = peopleList.GroupBy(person => person.Type)
                                                      .OrderBy(group => group.Key)
                                                      .Select(group => group.ToList())
                                                      .ToList();

Answer 1

Do you want to do it with LINQ?
You could use GroupBy and Average methods.

var groupedLists = peopleList.GroupBy(person => person.Type)
                             .OrderBy(group => group.Key)
                             .Select(group => new {
                                 People = group.ToList(),
                                 AverageScore = group.Average(p => p.ScorePercent)
                              })
                              .ToList();

Update

Assuming you want a list of Tuple<KindOfPerson, double>, here you go:

var scores = peopleList.GroupBy(p => p.Type)
                       .Select(g => Tuple.Create(g.Key, g.Average(p => p.ScorePercent)))
                       .ToList();

Creating a Dictionary<KindOfPerson, double> is very similar:

var scores = peopleList.GroupBy(p => p.Type)
                       .ToDictionary(g => g.Key, g => g.Average(p => p.ScorePercent));