VBA - How to tell 13 combinatios by randomize to remain under 100? - excel

Question

I would like to randomize 13 variables which in sum have to be 100%.
For a better understanding I show you what I mean by a snippet. From column F to column R all variables have to understand that in sum (column S) these are not allowed to be over 100.
Each row shall be another scenario, so the rows by itself are independent.
My approach was like the following but unfortunately nothing happens. Anyone an idea? Thanks a lot.
Sub Zufall()
Dim k As Integer
Application.ScreenUpdating = False
Range("F11:R55").ClearContents
DoEvents
Do Until WorksheetFunction.Sum(Range("S11:S55")) = 100
Randomize
For k = Columns(19) To Columns(6) Step -1
Cells(11, k).Formula = Int(Rnd() * 100)
Next k
Range("R55:F11").Value = WorksheetFunction.Sum(Range("S11:S55"))
DoEvents
Loop
Application.ScreenUpdating = True
End Sub

Answer 1

The following code shows how to generate a set of n random single precision numbers between 0 and 1 which sum to 1.
' Returns an array of random numbers (0 <= n < 1) which sum to 1.
' Size is the size of the array to return.
Function GenerateRandomNumbers(ByVal size As Integer) As Variant
ReDim vals(1 To size) As Single
Dim idx As Integer
Dim sum As Single
For idx = 1 To size
vals(idx) = Rnd
sum = sum + vals(idx)
Next idx
For idx = 1 To size
vals(idx) = vals(idx) / sum
Next idx
GenerateRandomNumbers = vals
End Function
You use it like this.
Sub Randomm()
Dim row As Long
Dim col As Long
Dim thirteenRandomNumbersWhichSumToOne As Variant
With Worksheets("Sheet1")
For row = 6 To 50
thirteenRandomNumbersWhichSumToOne = GenerateRandomNumbers(13)
For col = 6 To 18 ' F to R
.Cells(row, col).Value = thirteenRandomNumbersWhichSumToOne(col - 5)
.Cells(row, col).NumberFormat = "0%"
Next col
.Cells(row, 19).FormulaR1C1 = "=SUM(RC6:RC18)"
.Cells(row, 19).NumberFormat = "0%"
Next row
End With
End Sub

Answer 2

This will generate 13 values from A1 through A13:
Sub Randomm()
Dim wf As WorksheetFunction, rng As Range
Set wf = Application.WorksheetFunction
Set rng = Range("A1:A13")
rng.Formula = "=RAND()"
rng.Value = rng.Value
zum = wf.Sum(rng)
For i = 1 To 13
Cells(i, 1).Value = Cells(i, 1).Value / zum
Next i
rng.NumberFormat = "0.00%"
End Sub

Answer 3

this is the current and last code. Missing:
idx values in sum do not limit up to 100% in column S
Changed:
column S was implied by using the easy sum calcluation in Excel
the % wasnt shown right this is why i used it by Format in Excel
Sub Randomm()
Dim wf As WorksheetFunction, rng As Range, zum As Single, i As Integer
Set wf = Application.WorksheetFunction
Set rng = Range("F6:R50")
Dim totalRow As Single
rng.Formula = "=RANDBETWEEN(5,25)/100"
rng.Value = rng.Value
zum = wf.sum(rng)
For i = 6 To 50
Cells(i, 6).Value = Cells(i, 13).Value
Next i
End Sub
Function GenerateRandomNumbers(ByVal size As Integer) As Variant
ReDim vals(1 To size) As Single
Dim idx As Integer
Dim sum As Single
For idx = 1 To size
vals(idx) = Rnd
Next idx
For idx = 1 To size
vals(idx) = vals(idx)
Next idx
GenerateRandomNumbers = vals
End Function