Apply dynamically defined aggregation function on array values - vba

Question

I want apply a user defined aggregation function (string-value from a certain cell, like "SUM" or "STDEV") on an array of values. Here's a simplified example. However I don't know how to make the aggregation (last line):
Sub test()
Dim values() As Double
ReDim values(1 To 3)
values(1) = 3.5
values(2) = 5
values(3) = 4.8
Dim aggregate_fn As String
aggregate_fn = "SUM"
Dim result As Double
result = Evaluate("=" & aggregate_fn & "(" & values & ")") ' <-- This doesn't work, but hopefully it's clear what it should do
End Sub
EDIT
My original code is also creating the values array dynamically from a spreadsheet which uses , as decimal sign. This causes an issue with Scott's answer below.
Const datasht = "Daten"
Const aggregate_cell = "G1"
Sub run()
Dim sht As Worksheet
Dim n_rows As Integer
Dim rw As Integer
Application.DecimalSeparator = "."
Set sht = ActiveWorkbook.Worksheets(datasht)
n_rows = sht.Cells(1, 1).CurrentRegion.Rows.Count ' Get range of data
Dim values() As String
ReDim values(1 To n_rows)
For rw = 1 To n_rows
values(rw) = sht.Cells(rw, 1).Value
Next rw
Debug.Print (aggregate(values))
End Sub
Function aggregate(values() As String)
' Get aggregated value
Dim aggregate_fn As String
aggregate_fn = ActiveWorkbook.Worksheets(datasht).Range(aggregate_cell).Value
aggregate = Evaluate("=" & aggregate_fn & "(" & Join(values, ",") & ")") ' <-- doesn't work as intended
End Function

Answer 1

This should work for any function available via Application.WorksheetFunction, and is less likely to give an error if you pass too many values.
Sub Tester()
Dim arr(0 To 1000), res, x As Long, f as String
'get some values to work with...
For x = 0 To 1000
arr(x) = Rnd() * 10
Next x
f = "SUM"
res = CallByName(Application.WorksheetFunction, f, VbMethod, arr)
Debug.Print res
End Sub

Answer 2

I was able to get this to work by creating a string from your array, then using that instead:
Sub test()
Dim values() As Double
ReDim values(1 To 3)
values(1) = 3.5
values(2) = 5
values(3) = 4.8
Dim mystring As String, i As Long
mystring = values(LBound(values))
For i = LBound(values) + 1 To UBound(values)
mystring = mystring & "," & values(i)
Next i
Dim aggregate_fn As String
aggregate_fn = "SUM"
Dim result As Double
result = Evaluate("=" & aggregate_fn & "(" & mystring & ")")
Debug.Print result
End Sub

Answer 3

Join works with Strings change the values to String instead of Double:
Sub test()
Dim values() As String
ReDim values(1 To 3)
values(1) = 3.5
values(2) = 5
values(3) = 4.8
Dim aggregate_fn As String
aggregate_fn = "SUM"
Dim result As Double
result = Evaluate("=" & aggregate_fn & "(" & Join(values, ",") & ")")
Debug.Print result
End Sub
As per your edit there is no need for the array at all, just pass the range and worksheet to the function and use .Address on the range.
Const datasht = "Daten"
Const aggregate_cell = "G1"
Sub run()
Dim sht As Worksheet
Dim n_rows As Integer
Dim rw As Integer
'Application.DecimalSeparator = "."
Set sht = ActiveWorkbook.Worksheets(datasht)
n_rows = sht.Cells(1, 1).CurrentRegion.Rows.Count ' Get range of data
Dim rng As Range
Set rng = sht.Range(sht.Cells(1, 1), sht.Cells(n_rows, 1))
Debug.Print (aggregate(sht, rng))
End Sub
Function aggregate(sht As Worksheet, rng As Range)
' Get aggregated value
Dim aggregate_fn As String
aggregate_fn = sht.Range(aggregate_cell).Value
aggregate = sht.Evaluate("=" & aggregate_fn & "(" & rng.Address(1, 1) & ")")
End Function