Sum of gridview column considering unique ID/date

See more:

C#

ASP.NET

Hi. Is it possible to sum up a column in gridview BUT only getting value of unique Date column

Say, I have these values:

____________________
|   Date    | Value |
| 03/01/16  |   12  |
| 03/02/16  |   6   |
| 03/02/16  |   6   |
| 03/03/16  |   10  |

Total should be 12 +6+10 = 28
03/02/16 will not be summed up but will only get the value of one since the data repeats.

Regards

What I have tried:

I tried using gridview OnRowDataBound but it sums up all.

public Decimal TotalValue=0;
protected void gvLevel3OT_RowDataBound(object sender, GridViewRowEventArgs e)
{
    if (e.Row.RowType == DataControlRowType.DataRow)
    {
        TotalValue+= Convert.ToDecimal(e.Row.Cells[5].Text.ToString());
    }
    else if (e.Row.RowType == DataControlRowType.Footer)
    {
        e.Row.Cells[3].Text = "Total";
        e.Row.Cells[5].Text = TotalValue.ToString("F");
    }
}