Private Sub CommandButton3_Click()
Dim Col&, i&
Application.ScreenUpdating = False
Application.DisplayAlerts = False
For Col = 1 To 3 '3 colonnes dans l'exemple
For i = Cells(Rows.Count, Col).End(xlUp).Row To 2 Step -1
If Cells(i, Col) = Cells(i - 1, Col) Then Range(Cells(i, Col), Cells(i - 1, Col)).MergeCells = True
Next i
Next Col
Application.ScreenUpdating = True
Application.DisplayAlerts = True
End Sub