Combining fields from list of objects into a CSV

Question

LINQ newbie question.

I would like to combine fields into a comma separated list when others are same in a list of objects. Not sure if I put the question correctly.

  class A
{
    int id;
    int roll;
    string name;

    public A(int id, int roll, string name)
    {
        this.id = id;
        this.roll = roll;
        this.name = name;
    }
}

class Program
{
   static void Main(string[] args)
    {
        List<A> aList = new List<A>();
        A a1 = new A(24, 501, "alex");
        A a2 = new A(12, 27, "steven");
        A a3 = new A(24, 67, "bob");
        A a4 = new A(1, 90, "erin");
        A a5 = new A(12, 27, "christy");
        aList.Add(a1);
        aList.Add(a2);
        aList.Add(a3);
        aList.Add(a4);
        aList.Add(a5);

    }

Since id and roll of a2 and a5 are same (12, 27), when creating a new list of objects, I would like to have one of its fields as (12, 27, "steven,christy") and rest just copied since there wasn't any match.

I am sorry if the question/explanation is confusion.

Answer 1

var res = aList
    .GroupBy(z => new { z.id, z.roll })
    .Select(z => new A(z.Key.id, z.Key.roll, string.Join(",", z.Select(z2 => z2.name))))
    .ToList();

Do note id , roll and name will have to be public .