LINQ | Element Operator | First

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

First Operator

The First operator is used to return the first element of the given collection or sequence. Or it can also return the first element according to the given condition. This method can be overloaded in two different ways:

• First<TSource>(IEnumerable<TSource>): This method returns the first element of the given sequence or collection without any condition.
• First<TSource>(IEnumerable<TSource>, Func<TSource, Boolean>): This method returns the first element which specifies the given condition.

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.
• If the given collection or sequence does not contain any element in it, then this method will throw an InvalidOperationException.
• It will throw an error if the given collection or sequence does not contain any element that satisfies the given condition or it contains null.

Example 1:

// C# program to illustrate the
// use of First operator
using System;
using System.Linq;

class GFG {

    // Main Method
    static public void Main()
    {

        // Data source
        int[] sequence1 = {112, 44, 55,
                      66, 77, 777, 56};

        // Get the element which specifies
        // the given condition
        // Using First function
        var result1 = sequence1.First(seq => seq > 77);
        Console.WriteLine(result1);

        // If you try to run the commented part then
        // this part will give you InvalidOperationException
        // because the given sequence does not contain any element
        /*
           int[] sequence2 = {};
           var result2 = sequence2.First();
           Console.WriteLine(result2);
        */
    }
}

Output:

112

Example 2:

// C# program to find the name
// of the first 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 = "Anju", emp_gender = "Female",
                                  emp_hire_date = "17/6/2015", emp_salary = 50000},
        };

        // Query to find the name
        // the first employee Using
        // First method
        var res = emp.Select(e => e.emp_name).First();
        Console.WriteLine("Employee Name: {0}", res);
    }
}

Output:

Employee Name: Anjita