✅ LINQ, simple query

public record Course(
    string Title,
    string Category,
    int Number,
    DateOnly PublicationDate,
    TimeSpan Duration)
{
    public static readonly Course[] Catalog =
    [
        new Course(
            Title: "Elements of Geometry",
            Category: "MAT", Number: 101, Duration: TimeSpan.FromHours(3),
            PublicationDate: new DateOnly(2009, 5, 20)),
        new Course(
            Title: "Squaring the Circle",
            Category: "MAT", Number: 102, Duration: TimeSpan.FromHours(7),
            PublicationDate: new DateOnly(2009, 4, 1)),
        new Course(
            Title: "Recreational Organ Transplantation",
            Category: "BIO", Number: 305, Duration: TimeSpan.FromHours(4),
            PublicationDate: new DateOnly(2002, 7, 19)),
        new Course(
            Title: "Hyperbolic Geometry",
            Category: "MAT", Number: 207, Duration: TimeSpan.FromHours(5),
            PublicationDate: new DateOnly(2007, 10, 5)),
        new Course(
            Title: "Oversimplified Data Structures for Demos",
            Category: "CSE", Number: 104, Duration: TimeSpan.FromHours(2),
            PublicationDate: new DateOnly(2023, 11, 8)),
        new Course(
            Title: "Introduction to Human Anatomy and Physiology",
            Category: "BIO", Number: 201, Duration: TimeSpan.FromHours(12),
            PublicationDate: new DateOnly(2001, 4, 11)),
    ];
}

class Program
{
    public static void Main()
    {
        
        // all the courses that are 4hrs or longer grouped by their category. What is shown: Title, Course-Number, duration
        var q = Course.Catalog.Where(course => course.Duration.TotalHours >= 4).GroupBy(course => course.Category, course => new { course.Title, course.Number, course.Duration.TotalHours });
        q.Dump();
    }
}