Excel VBA - Determining Column or Row Target of Array UDF - arrays

Question

I have a simple excel UDF for converting an array of mass values to mol fractions. Most times, the output will be a column array (n rows by 1 column).
How, from within the VBA environment, do I determine the dimensions of the target cells on the worksheet to ensure that it should be returned as n rows by 1 column versus n columns by 1 row?
Function molPct(chemsAndMassPctsRng As Range)
Dim chemsRng As Range
Dim massPctsRng As Range
Dim molarMasses()
Dim molPcts()
Set chemsRng = chemsAndMassPctsRng.Columns(1)
Set massPctsRng = chemsAndMassPctsRng.Columns(2)
chems = oneDimArrayZeroBasedFromRange(chemsRng)
massPcts = oneDimArrayZeroBasedFromRange(massPctsRng)
'oneDimArrayZeroBasedFromRange is a UDF to return a zero-based array from a range.
ReDim molarMasses(UBound(chems))
ReDim molPcts(UBound(chems))
totMolarMass = 0
For chemNo = LBound(chems) To UBound(chems)
molarMasses(chemNo) = massPcts(chemNo) / mw(chems(chemNo))
totMolarMass = totMolarMass + molarMasses(chemNo)
Next chemNo
For chemNo = LBound(chems) To UBound(chems)
molPcts(chemNo) = Round(molarMasses(chemNo) / totMolarMass, 2)
Next chemNo
molPct = Application.WorksheetFunction.Transpose(molPcts)
End Function
I understand that, if nothing else, I could have an input parameter to flag if return should be as a row array. I'm hoping to not go that route.

Answer 1

Here is a small example of a UDF() that:
accepts a variable number of input ranges
extracts the unique values in those ranges
creates a suitable output array (column,row, or block)
dumps the unique values to the area
Public Function ExtractUniques(ParamArray Rng()) As Variant
Dim i As Long, r As Range, c As Collection, OutPut
Dim rr As Range, k As Long, j As Long
Set c = New Collection
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'
' First grab all the data and make a Collection of uniques
'
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On Error Resume Next
For i = LBound(Rng) To UBound(Rng)
Set r = Rng(i)
For Each rr In r
c.Add rr.Value, CStr(rr.Value)
Next rr
Next i
On Error GoTo 0
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'
' next create an output array the same size and shape
' as the worksheet output area
'
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k = 1
With Application.Caller
ReDim OutPut(1 To .Rows.Count, 1 To .Columns.Count)
End With
For i = LBound(OutPut, 1) To UBound(OutPut, 1)
For j = LBound(OutPut, 2) To UBound(OutPut, 2)
If k < c.Count + 1 Then
OutPut(i, j) = c.Item(k)
k = k + 1
Else
OutPut(i, j) = ""
End If
Next j
Next i
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'
' put the data on the sheet
'
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ExtractUniques = OutPut
End Function

Answer 2

You should return two dimensional arrays: n × 1 for row and 1 × n for column vectors.
So you need either
Redim molPcts(1, Ubound(chems) + 1)
or
Redim molPcts(Ubound(chems) + 1, 1)
To refer to them, you need to use both indices:
molPcts(1, chemNo + 1)
or
molPcts(chemNo + 1, 1)
If you prefer 0-based arrays, the redim should be like this:
Redim molPcts(0 To 0, 0 To Ubound(chems))
Redim molPcts(0 To Ubound(chems), 0 To 0)