Formula for for writing common numbers

[Grosso1280]

What formula will help me write common numbers from 2 cells? In cell A1 I have: 1,2,3. In cell B1 I have: 2,3,4. I would like cell C1 to write to me: 2 and 3.

[#2]

@Grosso1280 

Here is a custom VBA function:

Function Common(ByVal s1 As String, ByVal s2 As String) As String
    Dim a() As String
    Dim i As Long
    Dim r As String
    s1 = Replace(s1, " ", "")
    s2 = "," & Replace(s2, " ", "") & ","
    a = Split(s1, ",")
    For i = 0 To UBound(a)
        If InStr(s2, "," & a(i) & ",") Then
            r = r & "," & a(i)
        End If
    Next i
    If r <> "" Then
        Common = Mid(r, 2)
    End If
End Function

Use like this:

=Common(A1,B1)

[#3]

Thanks

[#4]

@Grosso1280 alternatively this formula should work (but it does return a blank because I reference the entire column instead of only the data set range):

=IFERROR(SORT(INDEX(B:B,UNIQUE(MATCH(A:A,B:B,0)))),"")

[#5]

@Grosso1280 

With formula that could be

=TEXTJOIN(",",1,
  XLOOKUP(
     FILTERXML("<r><n>" & SUBSTITUTE(A1,",","</n><n>") & "</n></r>",  "//n"),
     FILTERXML("<r><n>" & SUBSTITUTE(B1,",","</n><n>") & "</n></r>",  "//n"),
     FILTERXML("<r><n>" & SUBSTITUTE(B1,",","</n><n>") & "</n></r>",  "//n"),
""))