using System;

using System.Linq;

using System.Collections.Generic;

public class Program

{

    public static void Main()

    {

        var list = new List<MyObj>()

        {

            new MyObj { Id = 1, MyProp = true, Name = "A", Surname = "B"},

            new MyObj { Id = 2, MyProp = false, Name = "A", Surname = "B"},

            new MyObj { Id = 3, MyProp = true, Name = "B", Surname = "B"},

            new MyObj { Id = 4, MyProp = true, Name = "B", Surname = "B"},

            new MyObj { Id = 5, MyProp = true, Name = "C", Surname = "B"},

        }; 

​

        var query = list.Where(x => x.MyProp); 

        var groups = query.GroupBy(x => new { x.Name, x.Surname }).ToList();

        foreach (var group in groups)

        {

            DoSomethingWithGroup(group.Key, group);

        }

    }

​

    static void DoSomethingWithGroup<T>(T groupKey, IEnumerable<MyObj> entities)

    {

        Console.WriteLine(groupKey);

        foreach (var entity in entities)

        {

            Console.WriteLine($"- {entity.Id}");

        }

    }

}

​

class MyObj

{

    public bool MyProp { get; set; }

    public string Name { get; set; }

    public string Surname { get; set; }

    public int Id { get; set; }

}