C# Linq Contains Method

The Contains() method in LINQ is used to check whether a sequence contains a specific element. It returns true if the element is found, otherwise false. This method works with any IEnumerable<T> collection including arrays, lists, and queryable sequences.

Syntax

Following is the syntax for using Contains() with collections −

bool result = collection.Contains(element);

Following is the syntax for using Contains() with queryable sequences −

bool result = collection.AsQueryable().Contains(element);

Parameters

• element − The value to locate in the sequence.

Return Value

Returns true if the source sequence contains an element that has the specified value; otherwise, false.

Using Contains() with String Arrays

Example

using System;
using System.Linq;

class Demo {
    static void Main() {
        string[] arr = { "Java", "C++", "Python" };
        string str = "Python";
        bool res = arr.Contains(str);
        Console.WriteLine("Array contains Python? " + res);
        
        bool notFound = arr.Contains("JavaScript");
        Console.WriteLine("Array contains JavaScript? " + notFound);
    }
}

The output of the above code is −

Array contains Python? True
Array contains JavaScript? False

Using Contains() with Integer Lists

Example

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

class Demo {
    static void Main() {
        List<int> numbers = new List<int> { 10, 20, 30, 40, 50 };
        
        bool hasThirty = numbers.Contains(30);
        Console.WriteLine("List contains 30? " + hasThirty);
        
        bool hasSeventy = numbers.Contains(70);
        Console.WriteLine("List contains 70? " + hasSeventy);
    }
}

The output of the above code is −

List contains 30? True
List contains 70? False

Using Contains() with Custom Objects

When using Contains() with custom objects, the method uses the default equality comparer. For reference types, this compares object references, not values −

Example

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

class Student {
    public string Name { get; set; }
    public int Age { get; set; }
    
    public override bool Equals(object obj) {
        if (obj is Student other)
            return Name == other.Name && Age == other.Age;
        return false;
    }
    
    public override int GetHashCode() {
        return Name?.GetHashCode() ?? 0 ^ Age.GetHashCode();
    }
}

class Demo {
    static void Main() {
        List<Student> students = new List<Student> {
            new Student { Name = "Alice", Age = 20 },
            new Student { Name = "Bob", Age = 22 }
        };
        
        Student searchStudent = new Student { Name = "Alice", Age = 20 };
        bool found = students.Contains(searchStudent);
        Console.WriteLine("Found Alice? " + found);
    }
}

The output of the above code is −

Found Alice? True

Comparison: Contains() vs Any()

Conclusion

The LINQ Contains() method provides an efficient way to check if a collection contains a specific element. It works with all IEnumerable<T> collections and uses the default equality comparer, which can be customized by overriding Equals() and GetHashCode() methods in custom classes.