C#: Comparing two objects by multiple properties in SortedSet

Question

I'd like to compare two objects by multiple properties.

Let's say I have a class called Student, and every student has name and score. My wish is to create a SortedSet(implement a Comparer here), so whenever I add a Student into the collection they will be sorted by their score, and if they have the same score they will be sorted by their name alphabetically.

Java 8 equivalent of this would be:

TreeSet<Student> students = new TreeSet<>(
    Comparator.comparing(Student::getScore).thenComparing(Student::getName)
);

Is this possible using Comparer<Student>.Create() or in any other way?

Answer 1

You can use SortedSet with a custom comparer. Implementation is a little trickier:

var s = new SortedSet<Student>(
    Comparer<Student>.Create((a, b) => {
        // This code implements comparison by score first
        var res= a.Score.CompareTo(b.Score);
        // Ties are resolved by name in alphabetic order
        return res != 0 ? res : a.Name.CompareTo(b.Name);
    })
);

Answer 2

Two quick examples I put together, you could use an IComparer<> of type Student. You would then give it the comparisons in the order required, as such:

class Program
{
    static void Main(string[] args)
    {
        var set = new SortedSet<Student>(new StudentComparer());

        set.Add(new Student {Name = "Test", Score = 10});
        set.Add(new Student { Name = "Tom", Score = 5 });
        set.Add(new Student { Name = "Adam", Score = 90 });
        set.Add(new Student { Name = "Adam", Score = 85 });

        foreach (var setItem in set)
        {
            Debug.WriteLine($@"{setItem.Name} - {setItem.Score}");
        }

        /*  outputs:
            Tom - 5
            Test - 10
            Adam - 85
            Adam - 90
        */
    }

}

class Student
{
    public string Name { get; set; }
    public int Score { get; set; }
}

class StudentComparer : IComparer<Student>
{
    public int Compare(Student x, Student y)
    {
        var result = x.Score.CompareTo(y.Score); 

        if (result == 0)
        {
            result = x.Name.CompareTo(y.Name);
        }
        return result;
    }
}

You could also use a normal List, and use Linq:

        var students = new List<Student>
        {
            new Student {Name = "Test", Score = 10},
            new Student {Name = "Tom", Score = 5},
            new Student {Name = "Adam", Score = 90},
            new Student {Name = "Adam", Score = 85}
        };


        var orderedList = students.OrderByDescending(s => s.Score)
            .ThenBy(s => s.Name);

        foreach (var student in orderedList)
        {
            Debug.WriteLine($@"{student.Name} - {student.Score}");
        }

        /*  outputs:
            Adam - 90
            Adam - 85
            Test - 10
            Tom - 5
        */