LINQ Count

Summary: in this tutorial, you’ll learn how to use the LINQ Count() method to return the number of elements in a sequence.

Introduction to the LINQ Count() method

The LINQ Count() is an extension method that returns the number of elements in a sequence or the number that represent how many elements that satisfy a condition.

int Count<TSource> (
   this IEnumerable<TSource> source, 
   Func<TSource,bool> predicate
);Code language: C# (cs)

In this syntax:

• source in the input sequence with the IEnumerable<T>.
• predicate is a function to test each element for a specified condition.

The Count() function returns the number of elements or the number of elements that satisfy a condition.

LINQ Count() method examples

Let’s take some examples of using the LINQ Count() method.

1 ) Using the LINQ Count() method to count the number of elements in a sequence

The following program demonstrates how to use the Count() method to get the number of names whose lengths are less than or equal to 3:

using static System.Console;

var names = new string[] { "Alice", "Bob", "Peter", "David", "Ted" };

var shortNameCount = names.Count(name => name.Length <= 3);

WriteLine($"{shortNameCount} people have short names.");Code language: C# (cs)

Output:

2 people have short names.Code language: C# (cs)

2) Using the LINQ Count() method to count the elements that satisfy a condition

The following example uses the Count() method to get the number of employees in the IT department:

using System.Net.Http.Headers;
using static System.Console;

namespace LINQDemo
{
    class Employee
    {
        public string? Name { get; set; }
        public string? Department { get; set; }
        public int Salary { get; set; }

    }
    class Program
    {
        public static void Main()
        {
            var employees = new List<Employee>() {
                new() { Name = "John", Department = "HR", Salary = 50000 },
                new() { Name = "Jane", Department = "IT", Salary = 60000 },
                new() { Name = "Bob",  Department = "HR", Salary = 45000 },
                new() { Name = "Sara", Department = "IT", Salary = 55000 },
                new() { Name = "Tom",  Department = "IT", Salary = 65000 }
            };

            var result = employees.Count(e => e.Department == "IT");

            WriteLine($"The IT employee count: {result}");
           

        }
    }
}Code language: C# (cs)

Output:

The IT employee count: 3Code language: C# (cs)

How it works.

First, define the Employee class with three properties Name, Department, and Salary:

class Employee
{
    public string? Name { get; set; }
    public string? Department { get; set; }
    public int Salary { get; set; }

}Code language: C# (cs)

Second, define a list of Employee objects and initialize it with five elements:

var employees = new List<Employee>() 
{
    new() { Name = "John", Department = "HR", Salary = 50000 },
    new() { Name = "Jane", Department = "IT", Salary = 60000 },
    new() { Name = "Bob",  Department = "HR", Salary = 45000 },
    new() { Name = "Sara", Department = "IT", Salary = 55000 },
    new() { Name = "Tom",  Department = "IT", Salary = 65000 }
};Code language: C# (cs)

Third, count the number of employees in the IT department by using the Count() method:

var result = employees.Count(e => e.Department == "IT");Code language: C# (cs)

The lambda expression e => e.Department == “IT” tests each Employee object and returns true if the department of the employee is IT.

Finally, write the number of IT employees to the console:

WriteLine($"The IT employee count: {result}");Code language: C# (cs)

Summary

• Use the LINQ Count() method to get the number of elements in a sequence that satisfy a specified condition.