Random Numbers - Ensuring no duplicates

I've been having problems generating a series of five random numbers that I store into an integer array. My problem is that I don't know how to ensure that each random number is unique and not a duplicate of another within the array.

I'm trying this now with picking random numbers between 1 & 5 so at least that way, I can tell if I am getting duplicates within that range, in the hope that the array wil have store all numbers 1,2,3,4,5 just to prove that these numbers are chosen randomly, and without duplication.

Currently, I'm getting 2, 2, 4, 5, 1 , or whatever.

Any ideas or code out there that can help?

The only way i see to ensure a number isn't used yet is to loop through the used numbers and compare them with the randomly generated one.

if the limit of the random numbers is the same as the array (ie: elements 1-5 contain numbers 1-5 in random order), the best way by far is to fill the array in order, then randomly swap elements around.

I was just using 1 to 5 to test that it was not making duplicates.

Essentially, I could have over 1000 and need to pick 5. I just don't want to run the risk of duplication...

To be honest, though, I should have search before I posted as I've found an older thread that I've found to be extremely helpful.

Thanks, anyway.

Use the dictionary object.
For each number generated, check if its already in the dictionary, and if not, then add to the dictionary and add the number to your array or list or whatever you're doing.

That is the fastest and most efficient method of duplicate removal.

VB Code:

Option Explicit
 
Private Sub Form_Load()
    Dim i As Integer                    'Loop Counter
    Dim usedNumbers(50) As Integer      'hold the used numbers
    Dim CurrentNumber As Integer        'The current random number
    Dim j As Integer                    'Loop Counter
    Dim k As Integer                    'Holds our place in the UsedNumbers Array
    Dim BadNumber As Boolean            'Is it a bad number?
 
    For i = 0 To 49
        CurrentNumber = Int(Rnd() * 50) + 1
        'Ensure that you get numbers between 1 and 50   Int(Rnd() * 50) + 1
        For j = 0 To 49
            'Check the new number against every other number we've generated
            If (CurrentNumber = usedNumbers(j)) Then
                BadNumber = True
                Exit For
            End If
            
            If (usedNumbers(j) = 0) Then
                'We will only have zeroes in the array if no value has been entered
                'in used Numbers for that index so we can safely leave if we see a zero
                Exit For
            End If
        Next j
        
        While BadNumber
            'if its a bad number we need to keep generating randome numbers until we have  good one
            BadNumber = False
            CurrentNumber = Int(Rnd() * 50) + 1
            For j = 0 To 49
                'Do the same check to see if it is a bad number
                If (CurrentNumber = usedNumbers(j)) Then
                    BadNumber = True
                    Exit For
                End If
            Next j
        Wend
        'You won't get here unless you have a good number
        usedNumbers(k) = CurrentNumber
        k = k + 1
        
        Debug.Print CurrentNumber
    Next i
End Sub

Cheers...

Wrack , using your code i'll cut it a bit too long for me.

VB Code:

Option Explicit
 
Private Sub Form_Load()
    Dim i As Integer                    'Loop Counter
    Dim usedNumbers(50) As Integer      'hold the used numbers
    Dim CurrentNumber As Integer        'The current random number
    Dim j As Integer                    'Loop Counter
 
 
    For i = 0 To 49
        CurrentNumber = Int(Rnd() * 50) + 1
        'Ensure that you get numbers between 1 and 50   Int(Rnd() * 50) + 1
        For j = 0 To i ' only have to loop to the latest added
            'Check the new number against every other number we've generated
            If (CurrentNumber = usedNumbers(j)) Then
                j = i ' to get out of the inner for loop
                i = i -1 ' reset i to one lower cause it was a bad number
            End If
 
          If j <= i Then  ' number we don't have yet
             usedNumbers(i) = CurrentNumber
          End If
    Next i
End Sub

Here is an other option using a collection instead.

VB Code:

Private Sub Command1_Click()
Dim i As Integer
Dim col As Collection
Dim intIndex As Integer
Dim intArr(4) As Integer
 
'   Create a collection to hold all the numbers
    Set col = New Collection
 
'   Add the numbers to the collection
    For i = 1 To 5 '<=== 5 is for demo only.
        col.Add i
    Next i
    
    For i = 0 To 4
        Randomize
'       Find a random index from the
'       remaining collection memebers
        intIndex = Int(Rnd() * col.Count) + 1
        
'       Add the item to the array
        intArr(i) = col(intIndex)
        
'       Remove the item from the collection
'       so it isn't used again
        col.Remove intIndex
    Next i
    
'   Print the results
    Me.Cls
    For i = 0 To 4
        Me.Print intArr(i)
    Next i
End Sub