C# List GroupBy and Sum

    List<PartRequest> partRequests = new List<PartRequest>();
    partRequests.Add(new PartRequest()
    {
        factory = "f1",
        stock = "s1",
        material = "m1",
        quantity = 10
    });

    partRequests.Add(new PartRequest()
    {
        factory = "f1",
        stock = "s1",
        material = "m1",
        quantity = 20
    });

    partRequests.Add(new PartRequest()
    {
        factory = "f1",
        stock = "s2",
        material = "m1",
        quantity = 40
    });

    partRequests.Add(new PartRequest()
    {
        factory = "f2",
        stock = "s1",
        material = "m1",
        quantity = 10
    });
    partRequests.Add(new PartRequest()
    {
        factory = "f1",
        stock = "s1",
        material = "m2",
        quantity = 80
    });

    partRequests.Add(new PartRequest()
    {
        factory = "f2",
        stock = "s2",
        material = "m2",
        quantity = 120
    });

    partRequests.Add(new PartRequest()
    {
        factory = "f2",
        stock = "s2",
        material = "m2",
        quantity = 120
    });

    var materialGroup = partRequests.GroupBy(x => new { x.material }).Select(x =>   x.Key.material).ToList();

     var groupedResult = partRequests.GroupBy(x=>string.Join(x.factory,":",x.stock,":",x.material)).ToList();

    var groupByStckAndFactoryResult = partRequests.GroupBy(x => new { factory = x.factory, stock = x.stock})
        .Select(y => new { factory = y.Key.factory, stock = y.Key.stock, material = y.First().material }).ToList();

    var groupByStckAndFactoryAndMaterialResult = partRequests.GroupBy(x => new { factory = x.factory, stock = x.stock, material = x.material })
        .Select(y => new { factory = y.Key.factory, stock = y.Key.stock, material = y.Key.material, quantity = y.Sum(i => i.quantity) }).ToList();

    Console.WriteLine(materialGroup);