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Random Number Generator to Equal a Sum

Posted on 2011-03-08
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Last Modified: 2012-05-11
Hello Experts!

I am trying to create a VB code in 2010 that will take a sum (say 40), and randomly generate a set of random numbers (say 6 total numbers) that will equal that sum.  

For example, if I ran it one time, it would create:
8
7
5
9
6
5

and when I run it again, it would create:
7
10
4
8
3
8

I thank you all in advance!
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Question by:mmylius
8 Comments
 
LVL 39

Accepted Solution

by:
nutsch earned 250 total points
ID: 35076215
Hi, that macro should do it for you, everytime in a new sheet.

Sub GetRandom()
Dim sht As Worksheet, dblSum As Double, cl As range
application.screenupdating=false

Const lgTarget As Long = 40
Const lgNumbers As Long = 6

Set sht = ActiveWorkbook.Sheets.Add

With range("A1:A" & lgNumbers)
    .FormulaR1C1 = "=rand()"
    .Value = .Value

    dblSum = application.WorksheetFunction.Sum(range("A1:A" & lgNumbers))

    For Each cl In .Cells
        cl.Value = Round((cl.Value * lgTarget / dblSum), 0)
    Next
    
    .Cells(lgNumbers, 1).Value = lgTarget - application.WorksheetFunction.Sum(range("A1:A" & lgNumbers - 1))
End With

application.screenupdating=true

End Sub

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LVL 65

Expert Comment

by:RobSampson
ID: 35076428
Hi, that's a tough one!

This is VBScript, but you might be able to translate it to .NET.

Regards,

Rob.
intNumberToSumTo = 40
intNumbersRequired = 6

intLowerLimit = 1
intUpperLimit = intNumberToSumTo
strNumbers = ""
Randomize
For intNum = 1 To intNumbersRequired
	intUpperLimit = intUpperLimit - (intNumbersRequired + 1 - intNum)
	intNumber = Int((intUpperLimit - intLowerLimit) * Rnd + intLowerLimit)
	intUpperLimit = (intUpperLimit + (intNumbersRequired + 1 - intNum)) - intNumber
	If strNumbers = "" Then
		strNumbers = intNumber
	Else
		strNumbers = strNumbers & "," & intNumber
	End If
Next

MsgBox strNumbers

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LVL 65

Expert Comment

by:RobSampson
ID: 35076435
nutsch....nice one!
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LVL 53

Expert Comment

by:Bill Prew
ID: 35076448
Give this test a try.

Sub Test()
    MsgBox DoRand(30)
End Sub


Function DoRand(intNumber)
    Randomize
    intRemain = intNumber
    strList = ""
    While intRemain > 0
        intNext = Int((intRemain * Rnd) + 1)
        intRemain = intRemain - intNext
        If strList = "" Then
            strList = intNext
        Else
            strList = strList & "," & intNext
        End If
    Wend
    DoRand = strList
 End Function

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~bp
0
 
LVL 85

Expert Comment

by:Mike Tomlinson
ID: 35079872
That is a pretty cool answer by nutsch!

Here's another approach:
Option Explicit

Private Sub CommandButton1_Click()
    Dim randomSet As Variant
    randomSet = RandomSumSet(40, 6)
    
    ' ...do something with the set...
    ListBox1.Clear
    Dim i As Integer
    For i = LBound(randomSet) To UBound(randomSet)
        ListBox1.AddItem randomSet(i)
    Next
End Sub

Private Function RandomSumSet(ByVal sum As Integer, ByVal numDigits As Integer) As Variant
    Static Seeded As Boolean
    If Not Seeded Then
        Seeded = True
        Randomize
    End If
    
    Dim numbers() As Integer
    ReDim numbers(numDigits - 1)
    
    Dim startValue As Integer
    startValue = sum \ numDigits ' Integer Division
    
    Dim i As Integer
    For i = 1 To numDigits
        numbers(i - 1) = startValue
    Next
    If numDigits * startValue <> sum Then
        numbers(numDigits - 1) = sum - ((numDigits - 1) * startValue)
    End If
    
    Dim index As Integer
    Dim j As Integer
    For j = 1 To 100
        For i = 1 To numDigits
            Do
                index = Int((numDigits - 1 + 1) * Rnd + 1)
            Loop While index = i
            If Rnd >= 0.5 Then
                If numbers(i - 1) > 1 Then
                    numbers(i - 1) = numbers(i - 1) - 1
                    numbers(index - 1) = numbers(index - 1) + 1
                End If
            Else
                If numbers(index - 1) > 1 Then
                    numbers(index - 1) = numbers(index - 1) - 1
                    numbers(i - 1) = numbers(i - 1) + 1
                End If
            End If
        Next
    Next j
    
    RandomSumSet = numbers
End Function

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0
 
LVL 45

Expert Comment

by:patrickab
ID: 35081878
Cells A1:A6 contain =Randbetween(1,10) and A7 contains Sum(A1:A6). Code below and in the attached file.

Patrick
Sub rnandomnos()
While [A7] <> 40
Calculate
Wend
End Sub

To get a new set of numbers press F9 and then press the button

code below is in the attached file.

Patrick

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randNos.xls
0
 

Author Closing Comment

by:mmylius
ID: 35083605
nutsch, thank you very much, that was exactly what I was looking for!
0
 

Author Comment

by:mmylius
ID: 35083613
...going to fast.. thank you to everyone who answered also!
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