meter datos de id duplicados en una sola columna en un datagridview

for (int i = 0; i < dataGridView1.RowCount; i++)
{
     for (int j = 0; j < dataGridView1.ColumnCount; j++)
     {
         if (dataGridView1.Rows[i].Cells[j].Value != null)
         {
             for (int k = 0; k < dataGridView1.ColumnCount; k++)
             {
                 if (dataGridView1.Rows[i].Cells[j].Value.ToString() == dataGridView1.Rows[i].Cells[k].Value.ToString() && j != k)
                 {
                     dataGridView1.Rows[i].Cells[k].Value = "";
                 }
             }
         }

     }
}