LINQ | Element Operator | LastOrDefault

The element operators are used to return a single, or a specific element from the sequence or collection. For example, in a school when we ask, who is the principal? Then there will be only one person that will be the principal of the school. So the number of students is a collection and the principal is the only result that comes from the collection.

The LINQ Standard Query Operator supports 8 types of element operators:

  1. ElementAt
  2. ElementAtOrDefault
  3. First
  4. FirstOrDefault
  5. Last
  6. LastOrDefault
  7. Single
  8. SingleOrDefault

LastOrDefault Operator

The Last operator is used to return the last element of the collection or sequence. Or return the last element which specifies the given condition. Or return the default value if the given collection does not contain any element. It overcomes the InvalidOperationException problem of the Last method. This method can be overloaded in two different ways:

  • LastOrDefault<TSource>(IEnumerable<TSource>): This method returns the last element of a sequence, or a default value if the sequence contains no elements.
  • LastOrDefault<TSource>(IEnumerable<TSource>, Func<TSource, Boolean>): This method returns the last element of a sequence that satisfies a condition or a default value if no such element is found.

Important Points:

  • It does not support query syntax in C# and VB.Net languages.
  • It support method syntax in both C# and VB.Net languages.
  • It present in both the Queryable and Enumerable class.
  • The default value of the reference types and the nullable types is null.

Example 1:

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// C# program to illustrate the 
// use of LastOrDefault operator
using System;
using System.Linq;
using System.Collections.Generic;
  
class GFG {
  
    // Main Method
    static public void Main()
    {
  
        // Data source
        int[] sequence1 = {112, 44, 55, 66, 77, 777, 56};
        string[] sequence2 = {"Geeks", "GeeksforGeeks"};
        int[] sequence3 = {};
  
        // Get the element which specifies
        // the given condition Using the 
        // LastOrDefault(Condition) function
        var result1 = sequence1.LastOrDefault(seq => seq < 777);
          
        Console.WriteLine("Element: {0}", result1);
  
        // Get the only element of the sequence
        // Using LastOrDefault() function
        var result2 = sequence2.LastOrDefault();
          
        Console.WriteLine("Element: {0}", result2);
  
        // Get the default value
        var result3 = sequence3.LastOrDefault();
          
        Console.WriteLine("Default value: {0}", result3);
    }
}

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Output:

Element: 56
Element: GeeksforGeeks
Default value: 0

Example 2:

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// C# program to find the 
// id of the last employee
using System;
using System.Linq;
using System.Collections.Generic;
  
// Employee details
public class Employee {
  
    public int emp_id
    {
        get;
        set;
    }
  
    public string emp_name
    {
        get;
        set;
    }
  
    public string emp_gender
    {
        get;
        set;
    }
  
    public string emp_hire_date
    {
        get;
        set;
    }
  
    public int emp_salary
    {
        get;
        set;
    }
}
  
class GFG {
  
    // Main method
    static public void Main()
    {
        List<Employee> emp = new List<Employee>() {
              
            new Employee() {emp_id = 209, emp_name = "Anjita", emp_gender = "Female",
                                    emp_hire_date = "12/3/2017", emp_salary = 20000},
  
            new Employee() {emp_id = 210, emp_name = "Soniya", emp_gender = "Female",
                                    emp_hire_date = "22/4/2018", emp_salary = 30000},
  
            new Employee() {emp_id = 211, emp_name = "Rohit", emp_gender = "Male",
                                  emp_hire_date = "3/5/2016", emp_salary = 40000},
  
            new Employee() {emp_id = 212, emp_name = "Supriya", emp_gender = "Female",
                                      emp_hire_date = "4/8/2017", emp_salary = 40000},
  
            new Employee() {emp_id = 213, emp_name = "Anil", emp_gender = "Male",
                                emp_hire_date = "12/1/2016", emp_salary = 40000},
  
            new Employee() {emp_id = 214, emp_name = "Anupriya", emp_gender = "Female",
                                         emp_hire_date = "17/6/2015", emp_salary = 50000},
        };
  
        // Query to find the id of the last 
        // employee Using LastOrDefault method
        var res = emp.Select(e => e.emp_id).LastOrDefault();
          
        Console.WriteLine("Employee Id: {0}", res);
    }
}

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Output:

Employee Id: 214


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