Getting an enumerator that iterates through HashSet in C#

A HashSet in C# is a collection that stores unique elements without duplicates. To iterate through a HashSet, you can use the GetEnumerator() method which returns an enumerator object, or use a foreach loop for simpler iteration.

The HashSet<T>.Enumerator provides manual control over iteration using MoveNext() and Current properties, while foreach handles enumeration automatically behind the scenes.

Syntax

Following is the syntax for getting an enumerator from a HashSet −

HashSet<T>.Enumerator enumerator = hashSet.GetEnumerator();
while (enumerator.MoveNext()) {
    T current = enumerator.Current;
    // use current element
}

Alternatively, using foreach for automatic enumeration −

foreach (T element in hashSet) {
    // use element
}

Using GetEnumerator() Method

The GetEnumerator() method returns a HashSet<T>.Enumerator struct that implements the enumeration pattern with MoveNext() and Current −

using System;
using System.Collections.Generic;

public class Demo {
    public static void Main(String[] args) {
        HashSet<string> set1 = new HashSet<string>();
        set1.Add("A");
        set1.Add("B");
        set1.Add("C");
        set1.Add("D");
        set1.Add("E");
        set1.Add("F");
        set1.Add("G");
        set1.Add("H");
        Console.WriteLine("Elements in HashSet1...");
        foreach (string res in set1) {
            Console.WriteLine(res);
        }
        HashSet<string> set2 = new HashSet<string>();
        set2.Add("John");
        set2.Add("Jacob");
        set2.Add("Ryan");
        set2.Add("Tom");
        set2.Add("Andy");
        set2.Add("Tim");
        set2.Add("Steve");
        set2.Add("Mark");
        Console.WriteLine("Elements in HashSet2... (Enumerator iterating through HashSet)");
        HashSet<string>.Enumerator demoEnum = set2.GetEnumerator();
        while (demoEnum.MoveNext()) {
            string res = demoEnum.Current;
            Console.WriteLine(res);
        }
        Console.WriteLine("Is HashSet1 equal to HashSet2? = "+set1.Equals(set2));
        Console.WriteLine("Count of HashSet2 = "+set2.Count);
        set2.Clear();
        Console.WriteLine("Count of HashSet2 (updated) = "+set2.Count);
    }
}

The output of the above code is −

Elements in HashSet1...
A
B
C
D
E
F
G
H
Elements in HashSet2... (Enumerator iterating through HashSet)
John
Jacob
Ryan
Tom
Andy
Tim
Steve
Mark
Is HashSet1 equal to HashSet2? = False
Count of HashSet2 = 8
Count of HashSet2 (updated) = 0

HashSet with Duplicate Elements

HashSet automatically eliminates duplicate elements. When you add the same element multiple times, it stores only one copy −

using System;
using System.Collections.Generic;

public class Demo {
    public static void Main() {
        HashSet<string> set1 = new HashSet<string>();
        set1.Add("AB");
        set1.Add("CD");
        set1.Add("EF");
        set1.Add("AB");
        set1.Add("IJ");
        set1.Add("KL");
        set1.Add("EF");
        set1.Add("OP");
        Console.WriteLine("Elements in HashSet1");
        foreach(string val in set1) {
            Console.WriteLine(val);
        }
        HashSet<string> set2 = new HashSet<string>();
        set2.Add("EF");
        set2.Add("KL");
        Console.WriteLine("Elements in HashSet2... (Enumerator iterating through HashSet)");
        HashSet<string>.Enumerator demoEnum = set2.GetEnumerator();
        while (demoEnum.MoveNext()) {
            string res = demoEnum.Current;
            Console.WriteLine(res);
        }
        Console.WriteLine("Is set1 a superset of set2? "+set1.IsSupersetOf(set2));
    }
}

The output of the above code is −

Elements in HashSet1
AB
CD
EF
IJ
KL
OP
Elements in HashSet2... (Enumerator iterating through HashSet)
EF
KL
Is set1 a superset of set2? True

Comparison: GetEnumerator() vs foreach

Conclusion

The GetEnumerator() method provides manual control over HashSet iteration using MoveNext() and Current, while foreach offers a simpler approach. HashSet automatically handles duplicate elements by storing only unique values, making it ideal for collections where uniqueness is required.