Merge multiple GridView Rows and display as comma separated (delimited) in one single row in ASP.Net

Here I have created sample that will help you out.

HTML

<div>
    <asp:GridView ID="GridView1" runat="server" AutoGenerateColumns="false">
        <Columns>
            <asp:BoundField DataField="Name" HeaderText="Name" />
            <asp:BoundField DataField="product" HeaderText="Product" />
            <asp:BoundField DataField="price" HeaderText="Price" />
            <asp:BoundField DataField="Unit" HeaderText="Unit" />
        </Columns>
    </asp:GridView>
    <br />
    <asp:Button Text="Get Expected Output" runat="server" OnClick="GetOutput" />
    <br />
    <br />
</div>

Code

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

protected void GetOutput(object sender, EventArgs e)
{
    GridView gvResult = new GridView();
    gvResult.AutoGenerateColumns = true;
    gvResult.DataSource = GetResult((DataTable)ViewState["Data"]);
    gvResult.DataBind();
    this.form1.Controls.Add(gvResult);
}

private void BindGrid()
{
    DataTable dt = new DataTable();
    dt.Columns.AddRange(new DataColumn[4] { new DataColumn("Name", typeof(string)),
                        new DataColumn("product", typeof(string)),
                        new DataColumn("price",typeof(string)),
                        new DataColumn("Unit",typeof(string)) });
    dt.Rows.Add("John Hammond", "product1", "1256.25", "2");
    dt.Rows.Add("Mudassar Khan", "product2", "1852.28", "3");
    dt.Rows.Add("Robert Schidne", "product3", "1745.89", "1");
    ViewState["Data"] = dt;
    GridView1.DataSource = dt;
    GridView1.DataBind();
}

private DataTable GetResult(DataTable dt)
{
    DataTable result = dt.Clone();
    int i = 0;
    DataRow dr = result.NewRow();
    foreach (DataColumn column in dt.Columns)
    {
        string columnData = string.Empty;
        foreach (DataRow row in dt.Rows)
        {
            columnData += row.ItemArray[i].ToString() + ",";
        }
        dr[i] = columnData.Remove(columnData.Length - 1, 1);
        i++;
    }
    result.Rows.Add(dr);
    return result;
}

VB

Protected Sub Page_Load(sender As Object, e As EventArgs)
	If Not Me.IsPostBack Then
		BindGrid()
	End If
End Sub

Protected Sub GetOutput(sender As Object, e As EventArgs)
	Dim gvResult As New GridView()
	gvResult.AutoGenerateColumns = True
	gvResult.DataSource = GetResult(DirectCast(ViewState("Data"), DataTable))
	gvResult.DataBind()
	Me.form1.Controls.Add(gvResult)
End Sub

Private Sub BindGrid()
	Dim dt As New DataTable()
	dt.Columns.AddRange(New DataColumn(3) {New DataColumn("Name", GetType(String)), New DataColumn("product", GetType(String)), New DataColumn("price", GetType(String)), New DataColumn("Unit", GetType(String))})
	dt.Rows.Add("John Hammond", "product1", "1256.25", "2")
	dt.Rows.Add("Mudassar Khan", "product2", "1852.28", "3")
	dt.Rows.Add("Robert Schidne", "product3", "1745.89", "1")
	ViewState("Data") = dt
	GridView1.DataSource = dt
	GridView1.DataBind()
End Sub

Private Function GetResult(dt As DataTable) As DataTable
	Dim result As DataTable = dt.Clone()
	Dim i As Integer = 0
	Dim dr As DataRow = result.NewRow()
	For Each column As DataColumn In dt.Columns
		Dim columnData As String = String.Empty
		For Each row As DataRow In dt.Rows
			columnData += row.ItemArray(i).ToString() + ","
		Next
		dr(i) = columnData.Remove(columnData.Length - 1, 1)
		i += 1
	Next
	result.Rows.Add(dr)
	Return result
End Function

Screenshot