Group a List<object[]>

Question

I have a question that's similar to yesterday's question.
I've got this List<object[]>

List<object[]> olst = new List<object[]>();

olst.Add(new object[] { "AA1", "X", 1, 3.50 });
olst.Add(new object[] { "AA2", "Y", 2, 5.20 });
olst.Add(new object[] { "AA2", "Y", 1, 3.50 });
olst.Add(new object[] { "AA1", "X", 1, 3.20 });
olst.Add(new object[] { "AA1", "Y", 2, 5.30 });

I need to produce List<object[]> to hold this:

"AA1", "X", 2, 6.70
"AA2", "Y", 3, 8.70
"AA1", "Y", 2, 5.30

In other words, I need to group olst by the 1st and 2nd elements of each object[] and sum 3rd and 4th.
I could use a for loop, but I was hoping someone could help me using lambda expressions and/or linq to accomplish this.

Answer 1

List<object[]> olst = new List<object[]>();

            olst.Add(new object[] { "AA1", "X" });
            olst.Add(new object[] { "AA2", "Y" });
            olst.Add(new object[] { "AA2", "Y" });
            olst.Add(new object[] { "AA1", "X" });
            olst.Add(new object[] { "AA1", "Y" });

            var result = from ol in olst
                         group ol by new {p1 = ol[0], p2 = ol[1]}
                         into g
                         select g.First();

Something like this?

Answer 2

You need to group by an anonymous type, then sum the third and fourth columns:

List<object[]> grouped = olst
    .GroupBy(o => new { Prop1 = o[0].ToString(), Prop2 = o[1].ToString() })
    .Select(o => new object[] 
    {
        o.Key.Prop1,
        o.Key.Prop2,
        o.Sum(x => (int)x[2]),
        o.Sum(x => (double)x[3])
    })
    .ToList();