C# Linq LastorDefault Method

The LastOrDefault() method in C# LINQ returns the last element of a sequence, or a default value if the sequence is empty. This method prevents exceptions that would occur with Last() when called on empty collections.

Syntax

Following is the syntax for LastOrDefault() method −

public static T LastOrDefault<T>(this IEnumerable<T> source);
public static T LastOrDefault<T>(this IEnumerable<T> source, Func<T, bool> predicate);

Parameters

• source − The sequence to return the last element from.

• predicate − A function to test each element for a condition (optional).

Return Value

Returns the last element that satisfies the condition, or the default value for type T if no such element is found. For reference types, default is null. For value types like int, default is 0.

Using LastOrDefault() with Empty Collection

Example

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

class Demo {
    static void Main() {
        List<double> val = new List<double> { };
        double d = val.LastOrDefault();
        Console.WriteLine("Default Value = " + d);
        
        if (d == 0.0D) {
            d = 0.1D;
        }
        Console.WriteLine("Default Value changed = " + d);
    }
}

The output of the above code is −

Default Value = 0
Default Value changed = 0.1

Using LastOrDefault() with Non-Empty Collection

Example

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

class Program {
    static void Main() {
        List<int> numbers = new List<int> { 10, 20, 30, 40, 50 };
        
        int lastElement = numbers.LastOrDefault();
        Console.WriteLine("Last element: " + lastElement);
        
        List<string> names = new List<string> { "Alice", "Bob", "Charlie" };
        string lastName = names.LastOrDefault();
        Console.WriteLine("Last name: " + lastName);
    }
}

The output of the above code is −

Last element: 50
Last name: Charlie

Using LastOrDefault() with Predicate

Example

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

class Program {
    static void Main() {
        List<int> numbers = new List<int> { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 };
        
        // Find last even number
        int lastEven = numbers.LastOrDefault(x => x % 2 == 0);
        Console.WriteLine("Last even number: " + lastEven);
        
        // Find last number greater than 15 (doesn't exist)
        int lastGreaterThan15 = numbers.LastOrDefault(x => x > 15);
        Console.WriteLine("Last number > 15: " + lastGreaterThan15);
    }
}

The output of the above code is −

Last even number: 10
Last number > 15: 0

LastOrDefault() vs Last() Comparison

Conclusion

The LastOrDefault() method provides a safe way to retrieve the last element from a sequence without throwing exceptions on empty collections. It returns the appropriate default value when no matching element is found, making it ideal for scenarios where the sequence might be empty.