LINQ & Collections

C# LINQ Query Expressions & Grouping

Learn how to filter, transform, and group data collections in C# using Language Integrated Query (LINQ) fluent syntax and query syntax.

C# Source Code

Editable code sample with line numbers

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

public class Program {
    public class Student {
        public string Name { get; set; } = "";
        public string Department { get; set; } = "";
        public double Score { get; set; }
    }

public static void Main() {
        var students = new List<Student> {
            new Student { Name = "Alice", Department = "CS", Score = 92.5 },
            new Student { Name = "Bob", Department = "Math", Score = 78.0 },
            new Student { Name = "Charlie", Department = "CS", Score = 88.0 },
            new Student { Name = "Diana", Department = "Physics", Score = 95.0 },
            new Student { Name = "Evan", Department = "Math", Score = 84.5 }
        };

// 1. LINQ Filter and Order (Score >= 85)
        var highAchievers = students
            .Where(s => s.Score >= 85)
            .OrderByDescending(s => s.Score);

Console.WriteLine("High Achievers (Score >= 85):");
        foreach (var s in highAchievers) {
            Console.WriteLine($" - {s.Name} ({s.Department}): {s.Score}");
        }

// 2. LINQ Group by Department
        Console.WriteLine("\nDepartment Average Scores:");
        var deptAverages = students
            .GroupBy(s => s.Department)
            .Select(g => new {
                Department = g.Key,
                AvgScore = g.Average(s => s.Score),
                Count = g.Count()
            });

foreach (var dept in deptAverages) {
            Console.WriteLine($" - {dept.Department}: {dept.AvgScore:F1} (Students: {dept.Count})");
        }
    }
}

Expected Output

When this program is compiled and executed, the terminal outputs:

High Achievers (Score >= 85):
 - Diana (Physics): 95
 - Alice (CS): 92.5
 - Charlie (CS): 88

Department Average Scores:
 - CS: 90.2 (Students: 2)
 - Math: 81.3 (Students: 2)
 - Physics: 95.0 (Students: 1)

How the Code Works

LINQ enables declarative data querying over in-memory collections (IEnumerable<T>). The Where clause filters records lazily, OrderByDescending sorts, GroupBy partitions records by department key, and Average aggregates numeric fields in a concise, readable manner.

Time Complexity

O(N log N) due to sorting, O(N) for grouping

Space Complexity

O(N)

Key Takeaways & Best Practices

LINQ provides type safety and compile-time checking for complex transformations.
Deferred execution ensures queries execute only when iterated (e.g. in foreach or ToList()).

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Runnable Code

View Code

High Achievers (Score >= 85): - Diana (Physics): 95 - Alice (CS): 92.5 - Charlie (CS): 88 Department Average Scores: - CS: 90.2 (Students: 2) - Math: 81.3 (Students: 2) - Physics: 95.0 (Students: 1)

How the Code Works

Time Complexity

O(N log N) due to sorting, O(N) for grouping

Space Complexity

O(N)

Key Takeaways & Best Practices

LINQ provides type safety and compile-time checking for complex transformations.
Deferred execution ensures queries execute only when iterated (e.g. in foreach or ToList()).

C# LINQ Query Expressions & Grouping

C# Source Code

Expected Output

How the Code Works

Key Takeaways & Best Practices

Master C# with ZenCompiler

Related C# Examples

C# Binary Search Implementation

Python Program to Check Prime Number

Python Program for Fibonacci Series

Platform & Tools

Account

Company & Help

Legal & Policies

C# LINQ Query Expressions & Grouping

C# Source Code

Expected Output

How the Code Works

Key Takeaways & Best Practices

Master C# with ZenCompiler

Related C# Examples

C# Binary Search Implementation

Python Program to Check Prime Number

Python Program for Fibonacci Series