LINQ Basics

LINQ (Language Integrated Query) is one of the coolest features in C#. It lets you query and manipulate data collections using a clean, readable syntax. Once you get used to it, you will never want to go back to manual loops.

Basic LINQ Query

List<int> numbers = new List<int> { 5, 3, 8, 1, 9, 2, 7 };

// Get all even numbers
var evenNumbers = from n in numbers
                  where n % 2 == 0
                  select n;

foreach (int n in evenNumbers)
{
    Console.Write(n + " ");
}
// Output: 8 2

The query syntax looks a bit like SQL. from specifies the source, where filters items, and select determines what to return.

Method Syntax (Fluent API)

Most C# developers prefer method syntax because it is more concise and chains nicely:

List<string> names = new List<string>
{
    "Amina", "Bilal", "Chukwuemeka", "Fatima", "Emeka"
};

// Filter and transform
var shortNames = names
    .Where(n => n.Length <= 5)
    .OrderBy(n => n)
    .ToList();

foreach (string name in shortNames)
{
    Console.WriteLine(name);
}
// Output:
// Amina
// Bilal
// Emeka
// Fatima

The => is a lambda expression — an anonymous function. n => n.Length <= 5 means "for each n, return true if n.Length is less than or equal to 5."

Common LINQ Methods

List<int> numbers = new List<int> { 10, 25, 30, 45, 50 };

// First and Last
int first = numbers.First();        // 10
int last = numbers.Last();          // 50

// Sum, Average, Count
int sum = numbers.Sum();            // 160
double avg = numbers.Average();     // 32
int count = numbers.Count();        // 5

// Min and Max
int min = numbers.Min();            // 10
int max = numbers.Max();            // 50

// Any and All
bool hasLarge = numbers.Any(n => n > 40);   // true
bool allPositive = numbers.All(n => n > 0); // true

// Find
int found = numbers.Find(n => n > 20);  // 25 (first match)

These methods are incredibly useful. Instead of writing loops to find the sum, average, or minimum of a list, you just call a method. Clean and readable.

Chaining Operations

List<string> words = new List<string>
{
    "apple", "banana", "avocado", "blueberry", "apricot"
};

var result = words
    .Where(w => w.StartsWith("a"))      // Filter: starts with 'a'
    .OrderBy(w => w)                     // Sort alphabetically
    .Select(w => w.ToUpper())            // Transform to uppercase
    .ToList();

foreach (string word in result)
{
    Console.WriteLine(word);
}
// Output:
// APPLE
// APRICOT
// AVOCADO

The beauty of LINQ is how you chain operations together. Each method takes the output of the previous one and transforms it further. It reads almost like a sentence.