equals - C# SortedSet<T> and equality

Question

I am a bit puzzled about the behaviour of SortedSet, see following example:

public class Blah
{
    public double Value { get; private set; }

    public Blah(double value)
    {
        Value = value;
    }
}

public class BlahComparer : Comparer<Blah>
{
    public override int Compare(Blah x, Blah y)
    {
        return Comparer<double>.Default.Compare(x.Value, y.Value);
    }
}

public static void main()
{
    var blahs = new List<Blah> {new Blah(1), new Blah(2), 
                                new Blah(3), new Blah(2)}

    //contains all 4 entries
    var set = new HashSet<Blah>(blahs); 

    //contains only Blah(1), Blah(2), Blah(3)
    var sortedset = new SortedSet<Blah>(blahs, new BlahComparer());
}

So SortedSet discards entries if Compare(x,y) returns 0. Can I prevent this, such that my SortedSet behaves like HashSet and discards entries only if Equals() returns true?

Answer 1

Description

SortedSet: You have many elements you need to store, and you want to store them in a sorted order and also eliminate all duplicates from the data structure. The SortedSet type, which is part of the System.Collections.Generic namespace in the C# language and .NET Framework, provides this functionality.

According to MSDN Compare method returns

• Less than zero if x is less than y.
• Zero if x equals y.
• Greater than zero if x is greater than y.

More Information

• Dotnetperls - C# SortedSet Examples
• MSDN: Compare Method

Update

If your Bla class implements IComparable and you want your list sorted you can do this.

var blahs = new List<Blah> {new Blah(1), new Blah(2), 
                            new Blah(3), new Blah(2)};
blahs.Sort();

If your Bla class NOT implements IComparable and you want your list sorted you can use Linq (System.Linq namespace) for that.

blahs = blahs.OrderBy(x => x.MyProperty).ToList();