Linq query pivot specific columns to row

Question

I'm kinda new to linq.

But, let's say I have a table like this

ID	Names	Grade
30120	John Doe	12,5
30120	John Doe	15,75
30120	John Doe	10,52
30120	John Doe	10,23
30120	John Doe	13,89

and I want something like this

ID	Name	Grade 1	Grade 2	Grade 3	Grade 4	Grade 5
30120	John Doe	12,5	15,75	10,52	10,23	13,89

Would it be possible to fetch it using linq in C#?

Have you looked at Group By syntax yet? It would allow you to get a list of grades for each name. — blecovich, Aug 13 '21 at 02:50

score 0 · Accepted Answer · edited Aug 13 '21 at 14:19

You need to use groupBy, and a simple manual mapping:

class Program
{
    public class Course
    {
        public int Id { get; set; }
        public string Name { get; set; }
        public int Grade { get; set; }

    }
    static void Main(string[] args)
    {
        var courses = new List<Course>{
            new Course(){Id=30120,Name="John Doe",Grade=12},
            new Course(){Id=30120,Name="John Doe",Grade=13},
            new Course(){Id=30120,Name="John Doe",Grade=14},
            };

        var result = courses
                      .GroupBy(a => new { a.Id, a.Name })
                     .Select(m => Map(m));

        Console.WriteLine(JsonSerializer.Serialize(result));

    }

    private static object Map(IGrouping<dynamic, Course> arg1)
    {
        var course = new Dictionary<string, dynamic>();

        course.Add("Id", arg1.Key.Id);
        course.Add("Name", arg1.Key.Name);
        int index = 1;
        arg1.ToList().ForEach((p) =>
        {
            course.Add($"Grade{index++}", p.Grade);
        });

        return course;
    }
}

The only thing you need is to create a table from the dictionary.

Linq query pivot specific columns to row

1 Answers1