Check Duplicate data and remove it using LINQ Query in C#

This way:

HTML:

<form id="form1" runat="server">
    <div>
        <asp:GridView ID="gvName" runat="server">
        </asp:GridView>
        <br />
        <asp:GridView ID="gvUniqueName" runat="server">
        </asp:GridView>
    </div>
    </form>

C#:

 protected void Page_Load(object sender, EventArgs e)
    {
        if (!this.IsPostBack)
        {
            this.GetDistinctPersons();
        }
    }

    private void GetDistinctPersons()
    {
        DataTable dt = new DataTable();
        dt.Columns.AddRange(new DataColumn[4]{  
                            new DataColumn("ID", typeof(int)),
                            new DataColumn("FirstName", typeof(string )),  
                            new DataColumn("Desc", typeof(string)),
                            new DataColumn("Rupees", typeof(int))});

        dt.Rows.Add(1, "Test1", "Test", 100);
        dt.Rows.Add(2, "Test2", "Test", 100);
        dt.Rows.Add(3, "Test3", "Test", 100);
        dt.Rows.Add(1, "Test1", "Test", 100);
        dt.Rows.Add(2, "Test2", "Test", 500);

        this.gvName.DataSource = dt;
        this.gvName.DataBind();

        DataTable result = dt.AsEnumerable()
            .GroupBy(r => new
            {
                Col1 = r.Field<String>("FirstName")
            })
            .Select(g =>
            {
                var row = g.First();
                row.SetField("Rupees", g.Sum(r => r.Field<int>("Rupees")));
                return row;
            }).CopyToDataTable();
        this.gvUniqueName.DataSource = result;
        this.gvUniqueName.DataBind();
    }

Thank You

TRy This

 html

<div>
<asp:GridView ID="GridView1" runat="server">
</asp:GridView>
<br />
<asp:GridView ID="GridView2" runat="server">
</asp:GridView>
</div>

.cs

 DataTable dt = new DataTable();
        dt.Columns.AddRange(new DataColumn[4]{ new DataColumn("ID", typeof(int)),new DataColumn("name", typeof(string )),new DataColumn("desc", typeof(string)),new DataColumn("rupees", typeof(int))});
        dt.Rows.Add(1, "Test1", "Test", 1000);
        dt.Rows.Add(2, "Test2", "Test", 1000);
        dt.Rows.Add(3, "Test3", "Test", 1000);
        dt.Rows.Add(1, "Test1", "Test", 1000);
        dt.Rows.Add(2, "Test2", "Test", 1000);
        GridView1.DataSource = dt;
        GridView1.DataBind();

       DataTable newTable = dt.AsEnumerable().GroupBy(row => row.Field<int>("ID")).Select(g =>
        {
        DataRow first = g.First();
        if (g.Count() > 1)
        {
            int sum = g.Sum(r => r.Field<int>("rupees"));
            first.SetField("rupees", sum);
        }
        return first;
    })
    .CopyToDataTable();
        GridView2.DataSource = newTable;
        GridView2.DataBind();