calculating multiple cumulative frequency in gridview

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C#

ASP.NET

hi i need to calculate cumulative frequeccy like this:
a b c
1 2 2
1 3 5
1 6 11
2 4 4
2 1 5
2 5 10
3 2 2
3 4 6
but
for me the output is getting like this

a b c
1 2 2
1 3 5
1 6 11
2 4 4
2 1 5
2 5 10
3 2 12
3 4 16
my coding is:

ArrayList dataArray = new ArrayList();


   for (int rowIndex = gv1.Rows.Count - 2; rowIndex > 0; rowIndex--)
   {


   //for (int rowIndex = 1; rowIndex < gv1.Rows.Count; rowIndex++)
   //{

       //int rowIndex = gv1.Rows.Count;
       //GridViewRow row1 = gv1.Rows[rowIndex];
       GridViewRow previousRow = gv1.Rows[rowIndex + 1 ];
       int c1 = 0;
       int cv1 = 0;


       foreach (GridViewRow row1 in gv1.Rows)
       {
           //for (int i = 0; i < row1.Cells.Count; i++)
           //{

               if (row1.Cells[1].Text != previousRow.Cells[1].Text)
               {

                   //row2 = row1;
                   cv1 = System.Convert.ToInt32(row1.Cells[4].Text);
                   c1 += cv1;
                   row1.Cells[5].Text = c1.ToString();
                   dataArray.Add(c1);
               }

           //}
       }

       //break;
           }

can any one say me the suggestion for this