How to find duplicate row in Grid view

Try to filter this duplicate id / row in the query itself.
This would be the most optimized way of getting rid of duplicates.

It's not a good idea. Better handle those things in DataSource. Filter the data in DataSource(DataTable or something) & then bind it to GridView.

For your information
DataView.RowFilter Property[^]

Function findIDInGrid(ByVal array As ArrayList, ByVal s As String) As Integer
      Dim digit As Integer = -1
      For Each obj As Object In array
          If obj.ToString() = s Then
              digit = array.IndexOf(obj)
              Exit For
          End If
      Next

      Return digit
  End Function
  Protected Sub grdGoods_PreRender(ByVal sender As Object, ByVal e As System.EventArgs) Handles grdGoods.PreRender


      Try
          Dim array As New ArrayList

          For Each row As GridViewRow In grdGoods.Rows
              Dim rug_Id As Label = CType(row.FindControl("rug_Id"), Label)
              If findIDInGrid(array, rug_Id.Text) <> -1 Then
                  grdGoods.Rows(findIDInGrid(array, rug_Id.Text)).Visible = False
              End If
              array.Add(rug_Id.Text)
        
              End If
          Next
end sub