How to find duplicates value on gridview - asp.net

Question

I have a gridview data and want to highlight the duplicates values. I want to change all the duplicates value color become red.
gridview data:
ID | Items |
1 | Item1 | --> this will be red
2 | Item2 |
1 | Item1 | --> this will be red
1 | Item1 | --> this will be red
Protected Sub GridView1_RowDataBound(ByVal sender As GridView, ByVal e As System.Web.UI.WebControls.GridViewRowEventArgs) Handles GridView1.RowDataBound
If e.Row.RowType = DataControlRowType.DataRow Then
Dim idxPrev As Integer = e.Row.RowIndex - 1
If 1 <= e.Row.RowIndex Then
If e.Row.Cells(3).Text = sender.Rows(idxPrev).Cells(3).Text Then
e.Row.ForeColor = Drawing.Color.Red
sender.Rows(idxPrev).ForeColor = Drawing.Color.Red
End If
End If
End If
End Sub
my code only able to change a certain data, because I set the idxPrev only for the previous one, so it only change able to detect the previous index. I want it to check and change all of the gridview duplicates data. is it possible to do that? would you mind to help me to solve this problem?
Thanks in advances....

Answer 1

Try this please.
SOURCE
<asp:GridView ID="GridView1" HeaderStyle-BackColor="#3AC0F2" HeaderStyle-ForeColor="White" runat="server" AutoGenerateColumns="false">
<Columns>
<asp:BoundField DataField="Id" HeaderText="Id" ItemStyle-Width="30" />
<asp:BoundField DataField="Items" HeaderText="Items" ItemStyle-Width="150" />/>
</Columns>
</asp:GridView>
CODE BEHIND
protected void Page_Load(object sender, EventArgs e)
{
bind();
}
protected void bind()
{
con.Open();
SqlCommand cmd = con.CreateCommand();
cmd.CommandType = CommandType.Text;
cmd.CommandText = "select * from tblSample";
SqlDataAdapter da = new SqlDataAdapter(cmd);
DataSet ds = new DataSet();
da.Fill(ds);
GridView1.DataSource = ds;
GridView1.DataBind();
HighlightDuplicate(this.GridView1);
con.Close();
}
public void HighlightDuplicate(GridView gridview)
{
for (int currentRow = 0; currentRow < gridview.Rows.Count - 1; currentRow++)
{
GridViewRow rowToCompare = gridview.Rows[currentRow];
for (int otherRow = currentRow + 1; otherRow < gridview.Rows.Count; otherRow++)
{
GridViewRow row = gridview.Rows[otherRow];
bool duplicateRow = true;
if (int.Parse(rowToCompare.Cells[0].Text) != int.Parse(row.Cells[0].Text))
{
duplicateRow = false;
}
else if (duplicateRow)
{
rowToCompare.BackColor = Color.Red;
row.BackColor = Color.Red;
}
}
}
}
Add the following namespaces too in the code behind page.
using System.Data;
using System.Drawing;

Answer 2

/*highlight duplicate row in gridview */
public void HighlightDuplicate(GridView GridView1)
{
for (int ThisRow = 0; ThisRow < GridView1.Rows.Count - 1; ThisRow++)
{
Label lbl_cd = (Label)GridView1.Rows[ThisRow].FindControl("lblcd");
lblhidcd.Value = lbl_EmpCode.Text;
GridViewRow CompareRow =`enter code here` GridView1.Rows[ThisRow];
for (int NextRow = ThisRow + 1; NextRow < GridView1.Rows.Count; NextRow++)
{
GridViewRow row = GridView1.Rows[NextRow];
bool DuplicateRow = true;
Label lbl_cd1= (Label)GridView1.Rows[NextRow].FindControl("lblcd");
hidnxtrowhidcd.Value = lbl_cd1= .Text;
if ((lblhidcd.Value) == (hidnxtrowhidcd.Value ))
{
row.BackColor = System.Drawing.Color.BlanchedAlmond;
CompareRow.BackColor = System.Drawing.Color.BlanchedAlmond;
}
else if (DuplicateRow)
{
DuplicateRow = false;
}
}
}
}