Understanding C# LINQ Queries and Operations

Introduction to LINQ

LINQ (Language Integrated Query) is a powerful feature in C# that enables developers to query various data sources (like collections, databases, XML, etc.) in a concise and readable manner. This article provides practical examples of common LINQ queries and operations to help you understand how to utilize this feature in your C# applications.

Example 1: Basic LINQ Query

Let’s start with a simple example of querying a list of integers to find even numbers.

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

class Program
{
    static void Main()
    {
        List<int> numbers = new List<int> { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 };
        var evenNumbers = from num in numbers
                          where num % 2 == 0
                          select num;

        Console.WriteLine("Even Numbers:");
        foreach (var num in evenNumbers)
        {
            Console.WriteLine(num);
        }
    }
}

Explanation

• Data Source: A list of integers.
• Query: Select integers where the number is even.
• Output: Displays even numbers from the list.

Example 2: LINQ with Method Syntax

In addition to query syntax, LINQ also supports method syntax. Here’s how we can achieve the same result using method syntax:

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

class Program
{
    static void Main()
    {
        List<int> numbers = new List<int> { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 };
        var evenNumbers = numbers.Where(num => num % 2 == 0);

        Console.WriteLine("Even Numbers:");
        foreach (var num in evenNumbers)
        {
            Console.WriteLine(num);
        }
    }
}

Explanation

• Where Method: Filters the collection based on a predicate (even numbers).
• Output: Same as above, but using method syntax.

Example 3: Grouping Data

LINQ also allows you to group data. Here’s an example of grouping a list of names by their starting letter:

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

class Program
{
    static void Main()
    {
        List<string> names = new List<string> { "Alice", "Bob", "Charlie", "David", "Edward", "Frank" };
        var groupedNames = from name in names
                           group name by name[0] into nameGroup
                           select new { Initial = nameGroup.Key, Names = nameGroup };

        foreach (var group in groupedNames)
        {
            Console.WriteLine($"Names starting with '{group.Initial}': {string.Join(", ", group.Names)}");
        }
    }
}

Explanation

• Group By: Groups names by their initial letter.
• Output: Displays names sorted by their starting character.

Example 4: Joining Collections

Joining data from two collections is straightforward with LINQ. Here’s an example:

```csharp
using System;
using System.Collections.Generic;
using System.Linq;

class Program
{
static void Main()
{
List studentIds = new List { 1, 2, 3 };
List<(int Id, string Name)> students = new List<(int Id, string Name)>
{
(1, “Alice"),
(2, “Bob"),
(3, “Charlie")
};

    var studentInfo = from id in studentIds
                      join student in students on id equals student.Id
                      select student;

    foreach (var student in studentInfo)
    {
        Console.WriteLine($