how to merge cells in datagridview using vb.net

'e.g. Vertically merge the same cells of the fourth column

provide column index in below code to merge the cells

 
  Private Sub DataGridView1_CellPainting(ByVal sender As System.Object, ByVal e As System.Windows.Forms.DataGridViewCellPaintingEventArgs) Handles DataGridView1.CellPainting

        If e.ColumnIndex = 3 AndAlso e.RowIndex <> -1 Then

            Using gridBrush As Brush = New SolidBrush(Me.DataGridView1.GridColor), backColorBrush As Brush = New SolidBrush(e.CellStyle.BackColor)

                Using gridLinePen As Pen = New Pen(gridBrush)
                    ' Clear cell
                    e.Graphics.FillRectangle(backColorBrush, e.CellBounds)

                    ' Draw line (bottom border and right border of current cell)
                    'If next row cell has different content, only draw bottom border line of current cell
                    If e.RowIndex < DataGridView1.Rows.Count - 2 AndAlso DataGridView1.Rows(e.RowIndex + 1).Cells(e.ColumnIndex).Value.ToString() <> e.Value.ToString() Then
                        e.Graphics.DrawLine(gridLinePen, e.CellBounds.Left, e.CellBounds.Bottom - 1, e.CellBounds.Right - 1, e.CellBounds.Bottom - 1)
                    End If

                    ' Draw right border line of current cell
                    e.Graphics.DrawLine(gridLinePen, e.CellBounds.Right - 1, e.CellBounds.Top, e.CellBounds.Right - 1, e.CellBounds.Bottom)

                    ' draw/fill content in current cell, and fill only one cell of multiple same cells
                    If Not e.Value Is Nothing Then
                        If e.RowIndex > 0 AndAlso DataGridView1.Rows(e.RowIndex - 1).Cells(e.ColumnIndex).Value.ToString() = e.Value.ToString() Then
                        Else
                            e.Graphics.DrawString(CType(e.Value, String), e.CellStyle.Font, Brushes.Black, e.CellBounds.X + 2, e.CellBounds.Y + 5, StringFormat.GenericDefault)
                        End If
                    End If

                    e.Handled = True
                End Using
            End Using
        End If
    End Sub