Random Number within a range without repetition in VBA

Question

What would be the VBA code in excel to generate ONE random number between 1 to 100 that is displayed in a given cell (say A1) upon clicking a button, and then when the button is clicked again, it generates another random number between 1 to 100, THAT IS NOT A REPETITION. Ideally, this should allow me to click the button a 100 times and get all the numbers between 1-100 exactly once each ?

Answer 1

Technically there is no such thing as random numbers with no repetition. What you are asking for is actually a random permutation of a set of values, like the ordering of a shuffled deck of cards or lottery ball picks. Random permutation of a range of vlaues can be achieved in Excel VBA succinctly.

Assign your button's macro to RangeValue():

Public Sub RangeValue()
    Dim i As Long
    Static n As Long, s As String
    Const MIN = 1, MAX = 100, OUT = "A1", DEL = "."
    Randomize
    Do
        i = Rnd * (MAX - MIN) + MIN
        If 0 = InStr(s, i & DEL) Then
            n = n + 1: s = s & i & DEL
            Range(OUT) = i
            If n > MAX - MIN Then n = 0: s = ""
            Exit Do
        End If: DoEvents
    Loop
End Sub

That's it. The above code is all that is required to answer your question as posed.

You can use the Const line near the top to edit the MIN and MAX range of values that will be spun through randomly. You can also adjust the OUTput cell.

Once all of the values have been output (i.e. 100 button clicks), the code resets and spins through the range again in a new, random order. This continues forever. You can disable multiple spins-through by deleting this line: If n > MAX - MIN Then n = 0: s = ""

How does this work?

The routine maintains a string of previously output values. Each time the procedure is run, it selects a new random value from the range and checks if that value is already logged in the string. If it is it picks a new value and looks again. This continues in a loop until a value not currently logged in the string is randomly selected; that value is logged and output to the cell.

EDIT #1

To address your new question about how to set this up so that it works in more than one cell with different value ranges, assign your button's macro to ButtonClick():

Public Sub ButtonClick()
    Static n1 As Long, s1 As String, n2 As Long, s2 As String
    RangeValue 1, 100, "A1", n1, s1
    RangeValue 1, 150, "B1", n2, s2
End Sub

Private Sub RangeValue(MIN As Long, MAX As Long, OUT As String, n As Long, s As String)
    Dim i As Long
    Const DEL = "."
    Randomize
    Do
        i = Rnd * (MAX - MIN) + MIN
        If 0 = InStr(s, i & DEL) Then
            n = n + 1: s = s & i & DEL
            Range(OUT) = i
            If n > MAX - MIN Then n = 0: s = ""
            Exit Do
        End If: DoEvents
    Loop
End Sub

EDIT #2

While the above methods are concise, we can be more efficient by permuting the set of values in an array, and by avoiding the selection of values that have already been output. Here is a version that uses Durstenfeld's implementation of the Fisher–Yates shuffle algorithm:

Public Sub ButtonClick()
    Static n As Long, a
    Const MIN = 1, MAX = 100, OUT = "A1"
    If n = 0 Then a = Evaluate("transpose(row(" & MIN & ":" & MAX & "))"): n = UBound(a)
    PermuteArray a, n: Range(OUT) = a(n): n = n - 1
End Sub
Private Sub PermuteArray(a, n As Long)
    Dim j As Long, t
    Randomize
    j = Rnd * (n - 1) + 1
    If j <> n Then t = a(j): a(j) = a(n): a(n) = t
End Sub

Fisher–Yates has the advantage that it can be stopped and started as needed and so I am using it on the fly to permute the next value to display on each button click.

And to round this out with a version to use with your scenario of two output cells that use different value ranges:

Public Sub ButtonClick()
    Static n1 As Long, n2 As Long, a1, a2
    Const MIN1 = 1, MAX1 = 100, OUT1 = "A1"
    Const MIN2 = 1, MAX2 = 150, OUT2 = "B1"
    If n1 = 0 Then Reset a1, n1, MIN1, MAX1
    If n2 = 0 Then Reset a2, n2, MIN2, MAX2
    PermuteArray a1, n1: Range(OUT1) = a1(n1): n1 = n1 - 1
    PermuteArray a2, n2: Range(OUT2) = a2(n2): n2 = n2 - 1
End Sub
Private Sub PermuteArray(a, n As Long)
    Dim j As Long, t
    Randomize
    j = Rnd * (n - 1) + 1
    If j <> n Then t = a(j): a(j) = a(n): a(n) = t
End Sub
Private Sub Reset(a, n As Long, MIN As Long, MAX As Long)
    a = Evaluate("transpose(row(" & MIN & ":" & MAX & "))"): n = UBound(a)
End Sub

EDIT #3

I decided to create a version of this that utilizes the "inside-out" variation of Fisher–Yates. This allows us to specify the array of range values and shuffle it at the same time, an elegant and even more efficient enhancement:

Public Sub ButtonClick()
    Const MIN = 1, MAX = 100, OUT = "A1"
    Static a, n&
    If n = 0 Then Reset a, n, MIN, MAX
    Range(OUT) = a(n): n = n - 1
End Sub
Private Sub Reset(a, n&, MIN&, MAX&)
    Dim i&, j&
    Randomize: n = MAX - MIN + 1: ReDim a(1 To n)
    For i = 1 To n
        j = Rnd * (i - 1) + 1: a(i) = a(j): a(j) = i - 1 + MIN
    Next
End Sub

And to expand on your requirement of two different output cells that each use different value ranges, I decided to craft a generalized solution that can be used for an arbitrary number of independent output cells each tied to its own value range:

Public Sub ButtonClick()
    Dim MIN, MAX, OUT, i
    Static a, n, z
    MIN = Array(1, 11, 200): MAX = Array(100, 20, 205): OUT = Array("A1", "B2", "C3")
    z = UBound(MIN)
    If Not IsArray(n) Then ReDim a(z): ReDim n(z)
    For i = 0 To z
        If n(i) = 0 Then Reset a(i), n(i), MIN(i), MAX(i)
        Range(OUT(i)) = a(i)(n(i)): n(i) = n(i) - 1
    Next
End Sub
Private Sub Reset(a, n, MIN, MAX)
    Dim i, j
    Randomize: n = MAX - MIN + 1: ReDim a(1 To n)
    For i = 1 To n
        j = Rnd * (i - 1) + 1: a(i) = a(j): a(j) = i - 1 + MIN
    Next
End Sub

While the above is setup for three outputs, simply adjust the MIN, MAX, and OUT arrays near the top to suit your needs.

Answer 2

Here's a button click handler that uses static variables to hold an array containing a random sequence of numbers from 1 to 100, as well as the current position/index within that array. The array is created by populating a collection with numbers from 1 to 100, then transferring each number to the array in a random order.

Sub Button1_Click()

    Static NumberArray As Variant
    Static intIndex As Long

    If Not IsArray(NumberArray) Then NumberArray = GetRandomArray()

    ' If we haven't reached the end of our sequence, get another number...
    If intIndex < 100 Then
        Sheets("Sheet1").Range("A1") = NumberArray(intIndex)
        intIndex = intIndex + 1
    End If

End Sub

Function GetRandomArray() As Variant

    Dim c As New Collection
    Dim a(99) As Long

    ' Seed the RNG...
    Randomize

    ' Add each number to our collection...
    Dim i As Long
    For i = 1 To 100
        c.Add i
    Next

    ' Transfer the numbers (1-100) to an array in a random sequence...
    Dim r As Long
    For i = 0 To UBound(a)
        r = Int(c.Count * Rnd) + 1  ' Get a random INDEX into the collection
        a(i) = c(r)                 ' Transfer the number at that index
        c.Remove r                  ' Remove the item from the collection
    Next

    GetRandomArray = a

End Function

Answer 3

Try this:

Dim Picks(1 To 100) As Variant
Dim which As Long

Sub Lah()
    Dim A As Range
    Set A = Range("A1")
    If A.Value = "" Then
        which = 1
        For i = 1 To 100
            Picks(i) = i
        Next i
        Call Shuffle(Picks)
    Else
        which = which + 1
        If which = 101 Then which = 1
    End If
    A.Value = Picks(which)
End Sub

Sub Shuffle(InOut() As Variant)
    Dim HowMany As Long, i As Long, J As Long
    Dim tempF As Double, temp As Variant

    Hi = UBound(InOut)
    Low = LBound(InOut)
    ReDim Helper(Low To Hi) As Double
    Randomize

    For i = Low To Hi
        Helper(i) = Rnd
    Next i


    J = (Hi - Low + 1) \ 2
    Do While J > 0
        For i = Low To Hi - J
          If Helper(i) > Helper(i + J) Then
            tempF = Helper(i)
            Helper(i) = Helper(i + J)
            Helper(i + J) = tempF
            temp = InOut(i)
            InOut(i) = InOut(i + J)
            InOut(i + J) = temp
          End If
        Next i
        For i = Hi - J To Low Step -1
          If Helper(i) > Helper(i + J) Then
            tempF = Helper(i)
            Helper(i) = Helper(i + J)
            Helper(i + J) = tempF
            temp = InOut(i)
            InOut(i) = InOut(i + J)
            InOut(i + J) = temp
          End If
        Next i
        J = J \ 2
    Loop
End Sub

EDIT#1

The code begins by examining the destination cell, A1. If the cell is empty the code:

1. creates an array of 100 values
2. randomizes that array
3. initializes a sequential counter
4. places the first element of the randomized array in A1

If the cell is not empty, the code just places the next element of the randomized array in A1.

If you want to restart the process, clear A1. This will re-shuffle the array.

Answer 4

Here is an approach that maintains a global collection of available numbers and places #N/A in cells below A100. The button's click() sub makes sure that the collection is initialized when it needs to be. In a standard code module (insert -> module) enter:

Public Available As Collection
Public Initialized As Boolean

Sub Initialize()
    Dim i As Long, n As Long
    Dim used(1 To 100) As Boolean

    Set Available = New Collection
    If Not Range("A1").Value < 1 Then
        n = Cells(Rows.Count, 1).End(xlUp).Row()
        For i = 1 To n
            used(Cells(i, 1).Value) = True
        Next i
    End If
    For i = 1 To 100
        If Not used(i) Then Available.Add i
    Next i
    Initialized = True
End Sub

Function NextRand()
    'assumes that Initialize() has been called
    Dim i As Long, num As Long
    i = Application.WorksheetFunction.RandBetween(1, Available.Count)
    num = Available.Item(i)
    Available.Remove i
    NextRand = num
End Function

Add a button, then in its event handler add the code to make it look something like: (the actual name depends on the button and if it is an Active-X button, a forms button or just a shape)

Private Sub CommandButton1_Click()
    If (Not Initialized) Or Range("A1").Value < 1 Then Initialize
    Dim i As Long, n As Long

    If Range("A1").Value < 1 Then
        Range("A1").Value = NextRand()
        Exit Sub
    End If
    n = 1 + Cells(Rows.Count, 1).End(xlUp).Row()
    If n > 100 Then
        Cells(n, 1).Value = CVErr(xlErrNA)
    Else
        Cells(n, 1).Value = NextRand()
    End If
End Sub

Answer 5

Consider sorting a list of 100 random numbers and keeping their initial index. I have two buttons (or labels), one to initialize the list and the other to show the next random value

with code like this:

Const RandomCount As Long = 100

Private m_seq() As Variant   ' Keep in memory the random numbers
Private m_current As Long    ' Keep in memory the last shown number

Private Sub initializeLabel_Click()
    Dim wk As Worksheet
    Set wk = Worksheets.Add(Type:=xlWorksheet)  'add a worksheet
    
    ReDim m_seq(1 To RandomCount, 1 To 2)  'Initialize a 2D array
    Dim i As Long
    For i = 1 To RandomCount   
        m_seq(i, 1) = i           'add values 1..100 to first column
        m_seq(i, 2) = Rnd()       'add random numbers to second column
    Next i
    'Output the array into the new worksheet
    wk.Range("A1").Resize(RandomCount, 2).Value2 = m_seq
    ' Sort the worksheet
    wk.Range("A1").Resize(RandomCount, 2).Sort wk.Range("B1")

    'Input the sorted values back into the array
    m_seq = wk.Range("A1").Resize(RandomCount, 2).Value2

    ' Delete the worksheet quietly
    Application.DisplayAlerts = False
    wk.Range("A1").Resize(RandomCount, 2).ClearContents
    wk.Delete
    Application.DisplayAlerts = True

    'Reset the UI        
    m_current = 0
    [A1].ClearContents
End Sub

Private Sub randomLabel_Click()
    m_current = m_current + 1
    If m_current > RandomCount Then m_current = 1
    [A1].Value2 = m_seq(m_current, 1)
End Sub

The values in the temporary worksheet look like this

and after the sort

of which the first column is used