group by - c# grouping list of list by index

Question

I am from python programming and just a little knowledge of c#. I would like to group the following:

    List<List<dynamic>> data = new List<List<dynamic>>();
    data.Add(new List<dynamic> {"a", "z", "m", 4});
    data.Add(new List<dynamic> {"b", "x", "n", 2});
    data.Add(new List<dynamic> {"b", "x", "n", 1});
    data.Add(new List<dynamic> {"c", "y", "n", 3});
    data.Add(new List<dynamic> {"a", "z", "m", 5});
    data.Add(new List<dynamic> {"a", "y", "m", 6});

How can I group the list of list above without using keys only by index? I want the output to be:

    {
     {"a", "z", "m", {4, 5}},
     {"b", "x", "n", {2, 1}},
     {"c", "y", "n", {3}},
     {"a", "y", "m", {6}}
    }

question from:https://stackoverflow.com/questions/65897852/c-sharp-grouping-list-of-list-by-index

Answer 1

I have used Dennis method.

var lstOutput=data.GroupBy(_ => (_[0], _[1], _[2]), _ => (_[0],_[1],_[2],_[3]))
            .Select(grp => {
                dynamic first=null;
                first = new List<dynamic>(){
                    grp.Key.Item1,
                    grp.Key.Item2,
                    grp.Key.Item3,
                    grp.ToList().Select(x=>x.Item4).ToList()
                };
                return first;
                }).ToList();