spgridview and collapsed grouping by - Webpart

protected override void RenderContents(HtmlTextWriter writer)
{
writer.Write(errorMessage);
writer.Write(DisplayScript());
EnsureChildControls();
RenderChildren(writer);
}

private string DisplayScript()
{
StringBuilder strCollapseScript = new StringBuilder();
strCollapseScript.Append("--script language='javascript'--");
strCollapseScript.Append("var rows = document.getElementsByTagName('tr');");
strCollapseScript.Append("var numRows = rows.length;");
strCollapseScript.Append("for (var i = 0; i < numRows; ++i) ");
strCollapseScript.Append("{");
strCollapseScript.Append("if (rows[i].getAttribute('isexp') != null && rows[i].getAttribute('isexp').toLowerCase() == 'true')");
strCollapseScript.Append("{");
strCollapseScript.Append("if(rows[i].firstChild.firstChild != null && rows[i].firstChild.firstChild.tagName.toLowerCase() == 'a')");
strCollapseScript.Append("{ ");
strCollapseScript.Append("if (rows[i].firstChild.firstChild.title.toLowerCase() == 'expand/collapse')");
strCollapseScript.Append("{");
strCollapseScript.Append("rows[i].firstChild.firstChild.fireEvent('onclick');");
strCollapseScript.Append("}");
strCollapseScript.Append("}");
strCollapseScript.Append("}");
strCollapseScript.Append("}");
strCollapseScript.AppendLine("--/script--");
Page.ClientScript.RegisterStartupScript(Page.GetType(), "SearchScript", strCollapseScript.ToString());
return string.Empty ;
}

replace -- with greater sign.