对 datagridview 中一列的不同值求和

Question

I have a datagridview with two columns like this:

 group | quantity
------------------------
   chest  |  3
   legs   |  7
   back   |  2
   chest  |  1
   back   |  5
   legs   |  2

What I'm trying to do is to get the sum of distinct group to a list and use that list for populate another datagridview.

So the result must be in this example:

   chest  |  4
   legs   |  9
   back   |  7
   

I've tried some linq query code but without any success.

How can I do it?

Here's some Linq queries I tried:

List<string> vv = dataGridView1.Rows.Cast<DataGridViewRow>()
    .Where(x => !x.IsNewRow)
    // either..
    .Where(x => x.Cells[7].Value != null)
    //..or or both
    .Select(x => x.Cells[7].Value.ToString())
    .Distinct()
    .ToList();

dataGridView6.DataSource = vv; 

EDIT

the group column is being auto filled after a selection of another column combobox, the quantity is filled manually. For the group by I found this code and works but throw an error if a cell is empty:

    var Sums = dataGridView1.Rows.Cast<DataGridViewRow>()
                  .GroupBy(row => row.Cells[7].Value.ToString()) // group column
                  .Select(g => new { User = g.Key, Sum = g.Sum(row => Convert.ToInt32(row.Cells[1].Value)) });
dataGridView6.DataSource = Sums.ToList(); 

Answer 1

ok, here the solution that works:

var Sums = dataGridView1.Rows.Cast<DataGridViewRow>()
          .Where(row => row.Cells[7].Value != null)
        .GroupBy(row => row.Cells[7].Value.ToString()) // group column
        .Select(g => new { User = g.Key, Sum = g.Sum(row => Convert.ToInt32(row.Cells[1].Value)) }); // quantity column

        dataGridView6.DataSource = Sums.ToList();