[2005] How to stop duplicate random numbers?

[Chael]

Hi, I have (as you probably know) been messing around with random numbers alot recently. I just quickly came up with a Lotto Number Generator there but I need a way to stiop geting duplicate results eg. I want
4, 7, 16, 42, 34, 9 instead of
4, 7, 7, 3, 46, 9.

I have a feeling this involves loop and i am not veryu good with loops so some assistance would be great tanks

[Chael]

Anyone got any ideas? i need this quite soon!

[gigemboy]

Use the Random class instead of Rnd(). You can also add the original items to an arraylist, then each number that is picked, just remove the item from the arraylist so it cant pick it again. This would require you to call Random.Next with the count of the items instead of using "50" hard coded....

[mrcrash]

Dim I, number As Integer
        Dim asked() As Boolean
 
        For I = 0 To whatever
            Do
                number = CInt(Rnd() * whatever)
 
            Loop Until asked(number) = False
            asked(number) = True
        Next

[gigemboy]

You deleted your post and added it under mine mrcrash, so now its out of order

Below is an example of using an arraylist, so you can just use the .Remove or .RemoveAt method in order to remove the item from the list so it isnt picked again, thus not giving you duplicates. It also uses the Random class instead of Rnd()...

'initializes arraylist with all numbers
        Dim LottoNumbers As New ArrayList
        For I As Integer = 0 To 49 Step 1
            LottoNumbers.Add(I + 1)
        Next
        Dim MyRandom As New Random
        'array to hold the picked numbers
        Dim Picked(5) As Integer
        For I As Integer = 0 To 5 Step 1
            'gets next random index using the random class
            Dim PickedIndex As Integer = MyRandom.Next(0, LottoNumbers.Count - 1)
            'sets value in picked array to the value at the picked index
            Picked(i) = CInt(LottoNumbers(PickedIndex))
            'removes index from the list so it cant be picked again
            LottoNumbers.RemoveAt(PickedIndex)
        Next
        'just displays results
        Dim ReturnString As String
        For Each Number As Integer In Picked
            ReturnString &= Number.ToString & " "
        Next
        MessageBox.Show(ReturnString)

[mrcrash]

Sorry....
I deleted it because the code i gave was wrong!

[Chael]

Error 1 Class 'System.Random' cannot be indexed because it has no default property. C:\Documents and Settings\Compaq_Owner\Local Settings\Application Data\Temporary Projects\WindowsApplication1\Form1.vb 36 31 WindowsApplication1

is the error I get with that

[Chael]

no, srry that was for mrcrashes code, gigemboy, even with that code (except without the display method because I already have one) I still get numbers the same... that time I got
17, 1, 3, 26, 46, 26

[sparrow1]

no, srry that was for mrcrashes code, gigemboy, even with that code (except without the display method because I already have one) I still get numbers the same... that time I got
17, 1, 3, 26, 46, 26

Hi Chael,

I saw the code of gigemboy as well and i changed a little bit so when you click a button your numbers will be shown in a label, but the most important the code is working!
Try this,

Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
        Dim MyNumbers As New ArrayList
        For I As Integer = 0 To 49 Step 1
            MyNumbers.Add(I + 1)
        Next
        Dim MyRandom As New Random
        'array to hold the picked numbers
        Dim Picked(5) As Integer
        For I As Integer = 0 To 5 Step 1
            'gets next random index using the random class
            Dim PickedIndex As Integer = MyRandom.Next(0, MyNumbers.Count - 1)
            Picked(i) = CInt(MyNumbers(PickedIndex))
            'removes index from the list so it cant be picked again
            MyNumbers.RemoveAt(PickedIndex)
        Next
        'just displays results
        Dim ReturnString As String
        For Each Number As Integer In Picked
            ReturnString &= Number.ToString & " "
        Next
        Label1.Text = (ReturnString)
    End Sub

Wkr,

sparrow1

[gigemboy]

I dont know how you got duplicates still, since the value at the picked index is removed as soon as it is assigned to the picked numbers, so that number is removed from the arraylist on the next loop, so there is no way to get that same number again, as Sparrow has even tested...

[jmcilhinney]

I doubt that it's really any different to what Gig posted but I made a Codebank submission on this some time ago. See my signature for a link.