excel - VBA - Write all possible combinations of 4 columns of data

Question

This question already has answers here:

Answer 1

Here's a generic approach which should work for any number of columns/values (within reason).

Example usage:

Sub ListCombinations()

Dim col As New Collection
Dim c As Range, sht As Worksheet, res
Dim i As Long, arr, numCols As Long

    Set sht = ActiveSheet
   'lists begin in A1, B1, C1, D1
    For Each c In sht.Range("A1:D1").Cells
        col.Add Application.Transpose(sht.Range(c, sht.cells(Rows.Count, c.column).End(xlup))) 
        numCols = numCols + 1
    Next c
    
    res = Combine(col, "~~")
    
    For i = 0 To UBound(res)
        arr = Split(res(i), "~~")
        sht.Range("H1").Offset(i, 0).Resize(1, numCols) = arr
    Next i

End Sub

Re-usable function:

'create combinations from a collection of string arrays
Function Combine(col As Collection, SEP As String) As String()

    Dim rv() As String
    Dim pos() As Long, lengths() As Long, lbs() As Long, ubs() As Long
    Dim t As Long, i As Long, n As Long, ub As Long
    Dim numIn As Long, s As String, r As Long, v, tmp()

    numIn = col.Count
    ReDim pos(1 To numIn)
    ReDim lbs(1 To numIn)
    ReDim ubs(1 To numIn)
    ReDim lengths(1 To numIn)
    t = 0
    For i = 1 To numIn  'calculate # of combinations, and cache bounds/lengths
        'handle cases where only one value in a column (not passed in as array)
        If Not TypeName(col(i)) Like "*()" Then
            ReDim tmp(1 To 1)
            tmp(1) = col(i)
            col.Remove i
            If i > col.Count Then
                col.Add tmp
            Else
                col.Add tmp, before:=i
            End If
        End If
        lbs(i) = LBound(col(i))
        ubs(i) = UBound(col(i))
        lengths(i) = (ubs(i) - lbs(i)) + 1
        pos(i) = lbs(i)
        t = IIf(t = 0, lengths(i), t * lengths(i))
    Next i
    ReDim rv(0 To t - 1) 'resize destination array

    For n = 0 To (t - 1)
        s = ""
        For i = 1 To numIn
            s = s & IIf(Len(s) > 0, SEP, "") & col(i)(pos(i)) 'build the string
        Next i
        rv(n) = s

        For i = numIn To 1 Step -1
            If pos(i) <> ubs(i) Then   'Not done all of this array yet...
                pos(i) = pos(i) + 1    'Increment array index
                For r = i + 1 To numIn 'Reset all the indexes
                    pos(r) = lbs(r)    '   of the later arrays
                Next r
                Exit For
            End If
        Next i
    Next n

    Combine = rv
End Function