Check if two SortedSet objects are equal in C#

In C#, checking if two SortedSet objects are equal involves understanding that SortedSet<T> uses reference equality by default with the Equals() method. This means two sets are considered equal only if they reference the same object in memory, not if they contain the same elements.

To properly check if two SortedSet objects contain the same elements, you need to use the SetEquals() method or implement custom comparison logic.

Using Equals() Method (Reference Equality)

The Equals() method checks if two SortedSet objects reference the same instance in memory −

using System;
using System.Collections.Generic;

public class Demo {
   public static void Main() {
      SortedSet<int> set1 = new SortedSet<int>();
      set1.Add(100);
      set1.Add(200);
      set1.Add(300);
      set1.Add(400);
      
      Console.WriteLine("Elements in SortedSet1...");
      foreach (int res in set1) {
         Console.WriteLine(res);
      }
      
      SortedSet<int> set2 = new SortedSet<int>();
      set2.Add(100);
      set2.Add(200);
      set2.Add(300);
      set2.Add(400);
      
      Console.WriteLine("Elements in SortedSet2...");
      foreach (int res in set2) {
         Console.WriteLine(res);
      }
      
      Console.WriteLine("Are both sets equal (reference)? = " + set1.Equals(set2));
      
      // Assign set1 to set2 (same reference)
      set2 = set1;
      Console.WriteLine("After assignment, are they equal? = " + set1.Equals(set2));
   }
}

The output of the above code is −

Elements in SortedSet1...
100
200
300
400
Elements in SortedSet2...
100
200
300
400
Are both sets equal (reference)? = False
After assignment, are they equal? = True

Using SetEquals() Method (Content Equality)

To check if two SortedSet objects contain the same elements, use the SetEquals() method −

using System;
using System.Collections.Generic;

public class Demo {
   public static void Main() {
      SortedSet<int> set1 = new SortedSet<int>();
      set1.Add(10);
      set1.Add(20);
      set1.Add(30);
      
      SortedSet<int> set2 = new SortedSet<int>();
      set2.Add(30);
      set2.Add(10);
      set2.Add(20);
      
      SortedSet<int> set3 = new SortedSet<int>();
      set3.Add(10);
      set3.Add(20);
      set3.Add(40);
      
      Console.WriteLine("Set1 contains: " + string.Join(", ", set1));
      Console.WriteLine("Set2 contains: " + string.Join(", ", set2));
      Console.WriteLine("Set3 contains: " + string.Join(", ", set3));
      
      Console.WriteLine("set1.SetEquals(set2): " + set1.SetEquals(set2));
      Console.WriteLine("set1.SetEquals(set3): " + set1.SetEquals(set3));
      Console.WriteLine("set1.Equals(set2): " + set1.Equals(set2));
   }
}

The output of the above code is −

Set1 contains: 10, 20, 30
Set2 contains: 10, 20, 30
Set3 contains: 10, 20, 40
set1.SetEquals(set2): True
set1.SetEquals(set3): False
set1.Equals(set2): False

Comparison of Equality Methods

Using LINQ for Content Equality

Another approach to check content equality is using LINQ's SequenceEqual() method −

using System;
using System.Collections.Generic;
using System.Linq;

public class Demo {
   public static void Main() {
      SortedSet<string> set1 = new SortedSet<string> {"apple", "banana", "cherry"};
      SortedSet<string> set2 = new SortedSet<string> {"cherry", "apple", "banana"};
      SortedSet<string> set3 = new SortedSet<string> {"apple", "banana"};
      
      Console.WriteLine("Set1: " + string.Join(", ", set1));
      Console.WriteLine("Set2: " + string.Join(", ", set2));
      Console.WriteLine("Set3: " + string.Join(", ", set3));
      
      Console.WriteLine("Using SetEquals():");
      Console.WriteLine("set1.SetEquals(set2): " + set1.SetEquals(set2));
      Console.WriteLine("set1.SetEquals(set3): " + set1.SetEquals(set3));
      
      Console.WriteLine("Using SequenceEqual():");
      Console.WriteLine("set1.SequenceEqual(set2): " + set1.SequenceEqual(set2));
      Console.WriteLine("set1.SequenceEqual(set3): " + set1.SequenceEqual(set3));
   }
}

The output of the above code is −

Set1: apple, banana, cherry
Set2: apple, banana, cherry
Set3: apple, banana
Using SetEquals():
set1.SetEquals(set2): True
set1.SetEquals(set3): False
Using SequenceEqual():
set1.SequenceEqual(set2): True
set1.SequenceEqual(set3): False

Conclusion

To check if two SortedSet objects are equal in C#, use SetEquals() for content equality (same elements) or Equals() for reference equality (same object instance). The SetEquals() method is generally more useful as it compares the actual elements rather than object references.