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LINQ Intersect Method in C# with Examples
In this article, I am going to discuss the LINQ Intersect Method using C# with Examples. Please read our previous article where we discussed the LINQ Except Method in C# with Examples. As part of this article, I am going to discuss the following pointers
- What is LINQ Intersect Method?
- Examples to Understand LINQ Intersect Method with Value Type
- What happens if any of the sequences is null while performing the Intersect Operation?
- LINQ Intersect() Method Example with String Array using C#
- LINQ Intersect Method with Complex Type in C#
- Using IEqualityComparer Comparer with LINQ Intersect Method in C#
- Using Anonymous Type with Intersect Method in C#
- Overriding Equals() and GetHashCode() Methods
- Implementing IEquatble<T> Interface
What is LINQ Intersect Method?
The LINQ Intersect Method in C# is used to return the common elements from both collections. The elements that are present in both data sources are going to be returned by Intersect Method. There are two overloaded versions available for the Intersect Method in C#. They are as follows.
The one and only difference between the above two LINQ Intersect methods is that the second overloaded version takes IEqualityComparer as an argument. That means when we are working with Complex Types, in order to work as expected, we can use the overloaded method which takes the IEqualityComparer parameter.
Examples to Understand LINQ Intersect Method with Value Type
Let us understand LINQ Intersect Method with an example. Please have a look at the below image. As you can see in the below image, here we have two integer data sources i.e. DataSource 1 and Data Source 2. DataSource 1 contains elements such as 1, 2, 3, 4, 5, and 6, and DataSource 2 contains elements such as 1, 3, 5, 8, 9, and 10. If we want to retrieve the elements such as 1, 3, and 5 which exist in both the data sources then we need to use the LINQ Intersect method.
LINQ Intersect() Method Example using Method and Query Syntax:
The following example shows the use of the LINQ Intersect() Method using both Method and Query Syntax to fetch the common elements that exist in both collections. In query syntax, there is no such operator called Intersect, so here we need to use the mixed syntax i.e. both the query and method syntax to achieve the same.
using System.Collections.Generic;
using System;
using System.Linq;
namespace LINQDemo
{
class Program
{
static void Main(string[] args)
{
List<int> dataSource1 = new List<int>() { 1, 2, 3, 4, 5, 6 };
List<int> dataSource2 = new List<int>() { 1, 3, 5, 8, 9, 10 };
//Method Syntax
var MS = dataSource1.Intersect(dataSource2).ToList();
//Query Syntax
var QS = (from num in dataSource1
select num)
.Intersect(dataSource2).ToList();
foreach (var item in MS)
{
Console.WriteLine(item);
}
Console.ReadKey();
}
}
} Run the application and you will see the output as 1 3 5.
What happens if any of the sequences is null while performing the Intersect Operation?
The Intersect Method will throw an exception if any of the sequences is null. In the below example, the second sequence is null and while performing the Intersect operation using the Intersect Method it will throw an exception.
using System.Collections.Generic;
using System;
using System.Linq;
namespace LINQDemo
{
class Program
{
static void Main(string[] args)
{
List<int> dataSource1 = new List<int>() { 1, 2, 3, 4, 5, 6 };
List<int> dataSource2 = null;
//Method Syntax
var MS = dataSource1.Intersect(dataSource2).ToList();
foreach (var item in MS)
{
Console.WriteLine(item);
}
Console.ReadKey();
}
}
} Now run the application and you will get the following exception.
LINQ Intersect() Method Example with String Array using C#:
Let us see the examples to understand how the Intersect Method works with string collection. Here, in the below example, we have two arrays of countries and our requirement is to return the common countries i.e. the countries which exist in both collections.
using System;
using System.Linq;
namespace LINQDemo
{
class Program
{
static void Main(string[] args)
{
string[] dataSource1 = { "India", "USA", "UK", "Canada", "Srilanka" };
string[] dataSource2 = { "India", "uk", "Canada", "France", "Japan" };
//Method Syntax
var MS = dataSource1.Intersect(dataSource2).ToList();
//Query Syntax
var QS = (from country in dataSource1
select country)
.Intersect(dataSource2).ToList();
foreach (var item in QS)
{
Console.WriteLine(item);
}
Console.ReadKey();
}
}
} Now run the application and you will get the following output.
As you can see it displays only India and Canada. If you look at our collections, then you can see the country “UK” is present in both collections but the Intersect method did not fetch that country. This is because the default comparer that is being used by the Intersect method is case-insensitive.
So if you want to ignore the case-sensitive then you need to use the other overloaded version of the Intersect() method which takes IEqualityComparer as an argument. So, modify the program as shown below where we pass StringComparer as an argument to the Intersect() method which will ignore the case sensitivity while comparing the values.
using System;
using System.Linq;
namespace LINQDemo
{
class Program
{
static void Main(string[] args)
{
string[] dataSource1 = { "India", "USA", "UK", "Canada", "Srilanka" };
string[] dataSource2 = { "India", "uk", "Canada", "France", "Japan" };
//Method Syntax
var MS = dataSource1.Intersect(dataSource2, StringComparer.OrdinalIgnoreCase).ToList();
//Query Syntax
var QS = (from country in dataSource1
select country)
.Intersect(dataSource2, StringComparer.OrdinalIgnoreCase).ToList();
foreach (var item in QS)
{
Console.WriteLine(item);
}
Console.ReadKey();
}
}
} Now run the application and it will display the data as expected as shown in the below image.
.
LINQ Intersect Method with Complex Type in C#:
The LINQ Intersect() Method like other Set Methods (such as Distinct, Expect) also works in a different manner when working with complex data types such as Product, Employee, Student, etc. Let us understand this with an example. Create a class file with the name Student.cs and then copy and paste the following code into it.
namespace LINQDemo
{
public class Student
{
public int ID { get; set; }
public string Name { get; set; }
}
}
This is a very simple student class with just two properties. Let’s say, we have the following two data sources.
As you can see in the above image, we have two collections of student data. And if you notice we have two students which are appeared in both collections. Our requirement is to fetch all the student names which are present in both collections. That is the common student’s names from both collections. To achieve the same modify the Main method of the Program class as follows. In the below example, from the first data source, we are fetching the student names by using the select method and then we use the Intersect method and then we fetching the student names from the second data source.
using System.Collections.Generic;
using System;
using System.Linq;
namespace LINQDemo
{
class Program
{
static void Main(string[] args)
{
List<Student> StudentCollection1 = new List<Student>()
{
new Student {ID = 101, Name = "Preety" },
new Student {ID = 102, Name = "Sambit" },
new Student {ID = 105, Name = "Hina"},
new Student {ID = 106, Name = "Anurag"},
};
List<Student> StudentCollection2 = new List<Student>()
{
new Student {ID = 105, Name = "Hina"},
new Student {ID = 106, Name = "Anurag"},
new Student {ID = 107, Name = "Pranaya"},
new Student {ID = 108, Name = "Santosh"},
};
//Method Syntax
var MS = StudentCollection1.Select(x => x.Name)
. Intersect(StudentCollection2.Select(y => y.Name)).ToList();
//Query Syntax
var QS = (from std in StudentCollection1
select std.Name)
. Intersect(StudentCollection2.Select(y => y.Name)).ToList();
foreach (var name in MS)
{
Console.WriteLine(name);
}
Console.ReadKey();
}
}
} When you run the above code, you will get the output as expected as shown in the below image:
More Complex Examples to Understand Linq Intersect Example:
Now our requirement is to select all the information of all the students who are present in both collections. In order to do this, let us modify the program class as shown below.
using System.Collections.Generic;
using System;
using System.Linq;
namespace LINQDemo
{
class Program
{
static void Main(string[] args)
{
List<Student> StudentCollection1 = new List<Student>()
{
new Student {ID = 101, Name = "Preety" },
new Student {ID = 102, Name = "Sambit" },
new Student {ID = 105, Name = "Hina"},
new Student {ID = 106, Name = "Anurag"},
};
List<Student> StudentCollection2 = new List<Student>()
{
new Student {ID = 105, Name = "Hina"},
new Student {ID = 106, Name = "Anurag"},
new Student {ID = 107, Name = "Pranaya"},
new Student {ID = 108, Name = "Santosh"},
};
//Method Syntax
var MS = StudentCollection1.Intersect(StudentCollection2).ToList();
//Query Syntax
var QS = (from std in StudentCollection1
select std).Intersect(StudentCollection2).ToList();
foreach (var student in MS)
{
Console.WriteLine($" ID : {student.ID} Name : {student.Name}");
}
Console.ReadKey();
}
}
} Once you run the application, then it will not display any data. This is because the default comparer which is used by the LINQ Intersect Method for comparison is only checked whether two object references are equal and not the individual property values of the complex object. And in this case, each student object has a different reference and hence it is not returning any student data. As we already discussed we can overcome this problem in many different ways. Let us understand each way one by one.
Using IEqualityComparer Comparer with LINQ Intersect Method in C#:
In this approach, we need to create a class and then we need to implement the IEqualityComparer interface and we need to provide the implementation for the Equals and GetHashCode method. So, create a class file with the name StudentComparer.cs and then copy and paste the following code into it.
using System.Collections.Generic;
namespace LINQDemo
{
public class StudentComparer : IEqualityComparer<Student>
{
public bool Equals(Student x, Student y)
{
return x.ID == y.ID && x.Name == y.Name;
}
public int GetHashCode(Student obj)
{
return obj.ID.GetHashCode() ^ obj.Name.GetHashCode();
}
}
}
Next, we need to create an instance of StudentComparer class and then we need to pass that instance to the Intersect method. So, modify the Main method of the Program class as follows.
using System.Collections.Generic;
using System;
using System.Linq;
namespace LINQDemo
{
class Program
{
static void Main(string[] args)
{
List<Student> StudentCollection1 = new List<Student>()
{
new Student {ID = 101, Name = "Preety" },
new Student {ID = 102, Name = "Sambit" },
new Student {ID = 105, Name = "Hina"},
new Student {ID = 106, Name = "Anurag"},
};
List<Student> StudentCollection2 = new List<Student>()
{
new Student {ID = 105, Name = "Hina"},
new Student {ID = 106, Name = "Anurag"},
new Student {ID = 107, Name = "Pranaya"},
new Student {ID = 108, Name = "Santosh"},
};
StudentComparer studentComparer = new StudentComparer();
//Method Syntax
var MS = StudentCollection1
.Intersect(StudentCollection2, studentComparer).ToList();
//Query Syntax
var QS = (from std in StudentCollection1
select std)
.Intersect(StudentCollection2, studentComparer).ToList();
foreach (var student in QS)
{
Console.WriteLine($" ID : {student.ID} Name : {student.Name}");
}
Console.ReadKey();
}
}
}
With the above changes in place, run the application and you will get the output as expected as shown in the below image.
Using Anonymous Type with Intersect Method in C#:
In this approach, we need to select all the individual properties to an anonymous type using the LINQ select operator or Select Extension Method. The following program does exactly the same thing.
using System.Collections.Generic;
using System;
using System.Linq;
namespace LINQDemo
{
class Program
{
static void Main(string[] args)
{
List<Student> StudentCollection1 = new List<Student>()
{
new Student {ID = 101, Name = "Preety" },
new Student {ID = 102, Name = "Sambit" },
new Student {ID = 105, Name = "Hina"},
new Student {ID = 106, Name = "Anurag"},
};
List<Student> StudentCollection2 = new List<Student>()
{
new Student {ID = 105, Name = "Hina"},
new Student {ID = 106, Name = "Anurag"},
new Student {ID = 107, Name = "Pranaya"},
new Student {ID = 108, Name = "Santosh"},
};
//Method Syntax
var MS = StudentCollection1.Select(x => new { x.ID, x.Name })
.Intersect(StudentCollection2.Select(x => new { x.ID, x.Name })).ToList();
//Query Syntax
var QS = (from std in StudentCollection1
select new {std.ID, std.Name })
.Intersect(StudentCollection2.Select(x => new { x.ID, x.Name })).ToList();
foreach (var student in MS)
{
Console.WriteLine($" ID : {student.ID} Name : {student.Name}");
}
Console.ReadKey();
}
}
} With the above changes in place, now run the application code again and you will get the output as expected as shown in the below image.
Overriding Equals() and GetHashCode() Methods within the Student Class
This is the third approach and in this approach, we need to override the Equals and GetHashCode() in the Student class. As we know, by default, any type (predefined or user-defined) .NET Framework is inherited from the Object class. That means the Student class is also inherited from the Object class. So, we can override the Equals() and GetHashCode() methods of the Object class within the Student class. So, modify the Student class as shown below. Here, we are overriding the Equals() and GetHashCode() methods.
namespace LINQDemo
{
public class Student
{
public int ID { get; set; }
public string Name { get; set; }
public override bool Equals(object obj)
{
//As the obj parameter type is object, so we need to
//cast it to Student Type
return this.ID == ((Student)obj).ID && this.Name == ((Student)obj).Name;
}
public override int GetHashCode()
{
//Get the ID hash code value
int IDHashCode = this.ID.GetHashCode();
//Get the string HashCode Value
//Check for null refernece exception
int NameHashCode = this.Name == null ? 0 : this.Name.GetHashCode();
return IDHashCode ^ NameHashCode;
}
}
}
Next, we need to modify the Main method of the Program class as shown below. Here, we need to use the overloaded version of the Intersect method which does not take any parameter.
using System.Collections.Generic;
using System;
using System.Linq;
namespace LINQDemo
{
class Program
{
static void Main(string[] args)
{
List<Student> StudentCollection1 = new List<Student>()
{
new Student {ID = 101, Name = "Preety" },
new Student {ID = 102, Name = "Sambit" },
new Student {ID = 105, Name = "Hina"},
new Student {ID = 106, Name = "Anurag"},
};
List<Student> StudentCollection2 = new List<Student>()
{
new Student {ID = 105, Name = "Hina"},
new Student {ID = 106, Name = "Anurag"},
new Student {ID = 107, Name = "Pranaya"},
new Student {ID = 108, Name = "Santosh"},
};
//Method Syntax
var MS = StudentCollection1.Intersect(StudentCollection2).ToList();
//Query Syntax
var QS = (from std in StudentCollection1
select std).Intersect(StudentCollection2).ToList();
foreach (var student in MS)
{
Console.WriteLine($" ID : {student.ID} Name : {student.Name}");
}
Console.ReadKey();
}
}
}
Now run the application and again, you will get the same output as the previous two examples as shown in the below image.
Implementing IEquatble<T> Interface in Student Class
This is the last approach and, in this approach, we need to implement the IEquatble<T> Interface in Student Class and we need to implement the Equals Method of the IEquatble<T> Interface and we also need to override the GetHashCode method of the Object class. So, modify the Student class as shown below.
using System;
namespace LINQDemo
{
public class Student : IEquatable<Student>
{
public int ID { get; set; }
public string Name { get; set; }
public bool Equals(Student other)
{
return this.ID.Equals(other.ID) && this.Name.Equals(other.Name);
}
public override int GetHashCode()
{
int IDHashCode = this.ID.GetHashCode();
int NameHashCode = this.Name == null ? 0 : this.Name.GetHashCode();
return IDHashCode ^ NameHashCode;
}
}
}
As you can see, here we have done two things. First, we implement the Equals method of the IEquatable interface and then we override the GetHashCode method of the Object class. With the above changes in place, now modify the Main Method of the Program class as shown below.
using System.Collections.Generic;
using System;
using System.Linq;
namespace LINQDemo
{
class Program
{
static void Main(string[] args)
{
List<Student> StudentCollection1 = new List<Student>()
{
new Student {ID = 101, Name = "Preety" },
new Student {ID = 102, Name = "Sambit" },
new Student {ID = 105, Name = "Hina"},
new Student {ID = 106, Name = "Anurag"},
};
List<Student> StudentCollection2 = new List<Student>()
{
new Student {ID = 105, Name = "Hina"},
new Student {ID = 106, Name = "Anurag"},
new Student {ID = 107, Name = "Pranaya"},
new Student {ID = 108, Name = "Santosh"},
};
//Method Syntax
var MS = StudentCollection1.Intersect(StudentCollection2).ToList();
//Query Syntax
var QS = (from std in StudentCollection1
select std).Intersect(StudentCollection2).ToList();
foreach (var student in MS)
{
Console.WriteLine($" ID : {student.ID} Name : {student.Name}");
}
Console.ReadKey();
}
}
}
Now, run the application and you will also get the same output as expected as shown in the below image.
In the next article, I am going to discuss the LINQ Union Method using C# with Examples. Here, in this article, I try to explain the LINQ Intersect Method in C# with Examples and I hope you enjoy this article.
