LINQ Element Operators

In LINQ (Language Integrated Query), element operators are used to work with individual elements of a sequence. Here’s a rundown of some common element operators. There are following element operators.

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

1. First

It returns the first element of a sequence that satisfies a specified condition or the first element if no condition is specified. it returns error.

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

public class Employee
{
    public int Id { get; set; }
    public string Name { get; set; }
    public bool IsActive { get; set; }
}
class Program
{
    static void Main()
    {
        var employees = new List<Employee>
        {
         new Employee { Id = 1, Name = "Rohatash", IsActive = true },
         new Employee { Id = 2, Name = "Mohit", IsActive = false },
         new Employee { Id = 3, Name = "Saurav", IsActive = true },
         new Employee { Id = 4, Name = "Jeet", IsActive = true }
        };

        var firstEmployee = employees.First();
        Console.WriteLine(firstEmployee.Name); // Output: Rohatash

        var firstEmployeecon = employees.First(e => !e.IsActive);
        Console.WriteLine(firstEmployeecon.Name); // Output: Mohit
    }
}

Example

2. FirstOrDefault

It returns the first element of a sequence that satisfies a specified condition, or a default value if no such element is found.

Example

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

public class Employee
{
    public int Id { get; set; }
    public string Name { get; set; }
    public bool IsActive { get; set; }
}
class Program
{
    static void Main()
    {
        var employees = new List<Employee>
        {
         new Employee { Id = 1, Name = "Rohatash", IsActive = true },
         new Employee { Id = 2, Name = "Mohit", IsActive = false },
         new Employee { Id = 3, Name = "Saurav", IsActive = true },
         new Employee { Id = 4, Name = "Jeet", IsActive = true }
        };

        var firstActiveEmployee = employees.FirstOrDefault(e => e.IsActive);
        Console.WriteLine(firstActiveEmployee.Name); // Output: Rohatash

        var noActiveEmployee = employees.FirstOrDefault(e => !e.IsActive);
        Console.WriteLine(noActiveEmployee?.Name); // Output: Mohit
    }
}

3. Last

It returns the last element of a sequence that satisfies a specified condition or the last element if no condition is specified.

Example

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

public class Employee
{
    public int Id { get; set; }
    public string Name { get; set; }
    public bool IsActive { get; set; }
}
class Program
{
    static void Main()
    {
        var employees = new List<Employee>
        {
         new Employee { Id = 1, Name = "Rohatash", IsActive = true },
         new Employee { Id = 2, Name = "Mohit", IsActive = false },
         new Employee { Id = 3, Name = "Saurav", IsActive = true },
         new Employee { Id = 4, Name = "Jeet", IsActive = true }
        };
        var lastEmployee = employees.Last();
        Console.WriteLine(lastEmployee.Name); // Jeet
    }
}

4. LastOrDefault

It returns the last element of a sequence that satisfies a specified condition, or a default value if no such element is found.

Example

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

public class Employee
{
    public int Id { get; set; }
    public string Name { get; set; }
    public bool IsActive { get; set; }
}
class Program
{
    static void Main()
    {
        var employees = new List<Employee>
        {
         new Employee { Id = 1, Name = "Rohatash", IsActive = true },
         new Employee { Id = 2, Name = "Mohit", IsActive = false },
         new Employee { Id = 3, Name = "Saurav", IsActive = true },
         new Employee { Id = 4, Name = "Jeet", IsActive = true }
        };

        var lastActiveEmployee = employees.LastOrDefault(e => e.IsActive);
        Console.WriteLine(lastActiveEmployee.Name); // Output: Jeet
    }
}

5. Single

It returns the only element of a sequence that satisfies a specified condition, or throws an exception if more than one element is found.

Example

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

public class Employee
{
    public int Id { get; set; }
    public string Name { get; set; }
    public bool IsActive { get; set; }
}
class Program
{
    static void Main()
    {
        var employees = new List<Employee>
        {
         new Employee { Id = 1, Name = "Rohatash", IsActive = true },
         new Employee { Id = 2, Name = "Mohit", IsActive = false },
         new Employee { Id = 3, Name = "Saurav", IsActive = true },
         new Employee { Id = 4, Name = "Jeet", IsActive = true }
        };
        
        var singleEmployee = employees.Single(e => e.Id == 3);
        Console.WriteLine(singleEmployee.Name); // Output: Saurav

        // This will throw an exception because no employee has Id 5
        // var nonExistentEmployee = employees.Single(e => e.Id == 5);
    }
}

6. SingleOrDefault

It returns the only element of a sequence that satisfies a specified condition, or a default value if no such element is found.

Example

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

public class Employee
{
    public int Id { get; set; }
    public string Name { get; set; }
    public bool IsActive { get; set; }
}
class Program
{
    static void Main()
    {
        var employees = new List<Employee>
        {
         new Employee { Id = 1, Name = "Rohatash", IsActive = true },
         new Employee { Id = 2, Name = "Mohit", IsActive = false },
         new Employee { Id = 3, Name = "Saurav", IsActive = true },
         new Employee { Id = 4, Name = "Jeet", IsActive = true }
        };

        var singleOrDefaultEmployee = employees.SingleOrDefault(e => e.Id == 3);
        Console.WriteLine(singleOrDefaultEmployee.Name); // Output: Saurav

        var nonExistentEmployee = employees.SingleOrDefault(e => e.Id == 5);
        Console.WriteLine(nonExistentEmployee?.Name); // Output: (No output, as the value is null)
    }
}

7. ElementAt

It returns the element at a specified index in a sequence.

Example

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

public class Employee
{
    public int Id { get; set; }
    public string Name { get; set; }
    public bool IsActive { get; set; }
}
class Program
{
    static void Main()
    {
        var employees = new List<Employee>
        {
         new Employee { Id = 1, Name = "Rohatash", IsActive = true },
         new Employee { Id = 2, Name = "Mohit", IsActive = false },
         new Employee { Id = 3, Name = "Saurav", IsActive = true },
         new Employee { Id = 4, Name = "Jeet", IsActive = true }
        };

        var employeeAtIndex = employees.ElementAt(2);
        Console.WriteLine(employeeAtIndex.Name); // Output: Saurav

        var employeeAtIndex1 = employees.ElementAt(10);
        Console.WriteLine(employeeAtIndex.Name); // Output: Error
    }
}

8. ElementAtOrDefault

It returns the element at a specified index in a sequence, or a default value if the index is out of range. returns null if the index is out of range.

Example

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

public class Employee
{
    public int Id { get; set; }
    public string Name { get; set; }
    public bool IsActive { get; set; }
}
class Program
{
    static void Main()
    {
        var employees = new List<Employee>
        {
         new Employee { Id = 1, Name = "Rohatash", IsActive = true },
         new Employee { Id = 2, Name = "Mohit", IsActive = false },
         new Employee { Id = 3, Name = "Saurav", IsActive = true },
         new Employee { Id = 4, Name = "Jeet", IsActive = true }
        };
        
        var employeeAtIndexOrDefault = employees.ElementAtOrDefault(2);
        Console.WriteLine(employeeAtIndexOrDefault.Name); // Output: Saurav

        var outOfRangeEmployee = employees.ElementAtOrDefault(10);
        Console.WriteLine(outOfRangeEmployee?.Name); // Output: (No output, as the value is null)
    }
}

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