Bonjour
solution via une macro. Attention la macro trie la feuille entrée (j'ai supposé que ce n'était pas une contrainte)
Sub aargh()
With Sheets("entrée")
dl = .Cells(Rows.Count, 1).End(xlUp).Row
.Range("A1:C" & dl).Sort key1:=.Range("A1"), order1:=xlAscending, key2:=.Range("B2"), order2:=xlAscending, Header:=xlYes
Set ws = Sheets("sortie")
ov = ""
ws.Cells.Clear
.Rows(1).Copy ws.Cells(1, 1)
k = 1
For i = 2 To dl
nv = .Cells(i, 1) & .Cells(i, 2)
If ov <> nv Then
k = k + 1
ws.Cells(k, 1) = .Cells(i, 1)
ws.Cells(k, 2) = .Cells(i, 2)
ov = nv
End If
ws.Cells(k, 3) = ws.Cells(k, 3) & "," & .Cells(i, 3)
Next i
End With
End Sub