Sub GrouperToutesLes300Lignes()
Dim c As Range, PLig&
PLig = 1
Application.ScreenUpdating = False
For Each c In Range(Cells(1), Cells(Rows.Count, 1).End(xlUp))
If c.Row Mod 300 = 0 Then
Range(Cells(PLig, 1), Cells(c.Row - 1, 1)).Rows.Group
PLig = c.Row + 1
End If
Next c
End Sub