[RESOLVED] Random from one listbox to another

[irishlad]

I have two listboxes and one text box. lbxData is already populated with strings (ex; car, boat, motorcycle) I have a text box (tbxRandom) for user input to choose the number of random strings they want generated and placed in the other listbox (lbxRandom) when clicking btnRandom. Here is what I have but keep getting an error. mylist.addrange(str) "value cannot be null. parameter name: collection

Dim Str As String

        'Declare a List 
        Dim myList As New List(Of String)

        'Mylist gets the values of the existing array
        myList.AddRange(Str)

        'Declare random
        Dim rnd As New System.Random

        'This holds the generated random number
        Dim randomNumber As Integer = 0

        Me.lbxRandom.Items.Clear()


        Dim count As Integer = 0

        'textbox for user to choose the number of randomly generated items
        If Integer.TryParse(tbxRandom.Text, count) Then

            'Keep looping until all items generated
            Do While count <> 0

                'Generate randomNumber 
                randomNumber = rnd.Next(0, myList.Count)

                'Add current item to listbox
                Me.lbxRandom.Items.Add(myList(randomNumber))

                'Remove the used item so it can't be used again
                myList.RemoveAt(randomNumber)

                'Reduce count by 1
                count -= 1
            Loop
        Else
            MessageBox.Show("Problem with that number you entered")
        End If

can anyone tell me what i'm doing wrong

[aashish_9601]

'Mylist gets the values of the existing array
        myList.AddRange(Str)

1) you have commented that Mylist gets the value from the array, but you have declared Str as an single variable

value cannot be null. parameter name: collection

2) since Str is only but declared but not initialized you are getting the error

[irishlad]

So how do I do that?

[ThomasJohnsen]

Try this:

Dim Str() As String = {"Item1", "Item2", "Item3", "Item4", "Item5"}
        Dim myList As New List(Of String)
        Dim rnd As New System.Random
        Dim randomNumber As Integer = 0
        Dim count As Integer = 0
 
        myList.AddRange(Str)
 
        Me.lbxRandom.Items.Clear()
 
        If Integer.TryParse(tbxRandom.Text, count) Then
 
            Do While count <> 0
 
                randomNumber = rnd.Next(0, myList.Count)
                Me.lbxRandom.Items.Add(myList(randomNumber))
                myList.RemoveAt(randomNumber)
                count -= 1
 
            Loop
 
        Else
            MessageBox.Show("Problem with that number you entered")
        End If

Tom

[irishlad]

That works great if creating a new 1 dimension array using items 1-5, but how do I create an array from a list of strings in the lbxdata listbox? I want to randomly choose a number (tbxrandom) from the lbxdata listbox and put that random list in the lbxRandom listbox. I tried changing to
Dim Str() as string=lbxdata.items.tostring but get a an error saying "Value of type string cannot be converted to 1-dimensional array of string"

[ThomasJohnsen]

Ok - I was trying to come up with a solution to post 2 and didn't read your initial post well enough apparently

Could this be what you're after:

Dim rnd As New System.Random
        Dim randomNumber As Integer = 0
        Dim count As Integer = 0
 
        Me.lbxRandom.Items.Clear()
 
        If Integer.TryParse(tbxRandom.Text, count) AndAlso count <= lbxData.Items.Count Then
 
            Do While count <> 0
 
                randomNumber = rnd.Next(0, lbxData.Items.Count)
                Me.lbxRandom.Items.Add(lbxData.Items(randomNumber))
                'Uncomment this line if you want the items deleted in lbxData
                'lbxData.Items.RemoveAt(randomNumber)
                count -= 1
 
            Loop
 
        Else
            MessageBox.Show("Problem with that number you entered")
        End If

[irishlad]

That works great, thank you so much for the help.

[dbasnett]

    Private Sub Form1_Load(sender As System.Object, _
                           e As System.EventArgs) Handles MyBase.Load
        lbxData.Items.AddRange(New String() {"car", "boat", "motorcycle", "truck", "plane", "submarine"})
    End Sub

    Dim PRNG As New System.Random 'note - declared in namespace

    Private Sub Button1_Click(sender As System.Object, _
                              e As System.EventArgs) Handles Button1.Click

        lbxRandom.Items.Clear()

        Dim count As Integer

        'textbox for user to choose the number of randomly generated items
        If Integer.TryParse(tbxRandom.Text, count) Then
            For x As Integer = 1 To count
                lbxRandom.Items.Add(lbxData.Items(PRNG.Next(lbxData.Items.Count)))
            Next
        Else
            MessageBox.Show("Problem with that number you entered")
        End If
    End Sub

Don't make this complicated. Also, the random should be declared in the namespace, not in the button.

[irishlad]

I know I resolved this because it appeared to be working. Which it does but I didn't notice that it removed items from the first listbox. with the line uncommented "'lbxData.Items.RemoveAt(randomNumber)" with it commented gives me repeats of the randomly selected items, which I don't want. I'm thinking i'm going to have to create an array from the first listbox then randomly select items from the array. Is this correct? If so how do you accomplish this???

[ThomasJohnsen]

I know I resolved this because it appeared to be working. Which it does but I didn't notice that it removed items from the first listbox. with the line uncommented "'lbxData.Items.RemoveAt(randomNumber)" with it commented gives me repeats of the randomly selected items, which I don't want. I'm thinking i'm going to have to create an array from the first listbox then randomly select items from the array. Is this correct? If so how do you accomplish this???

Let me see if I got this right - you wan't to add random items from one listbox to another. You wan't the items to not be removed from the first listbox on a runthrough, but yet they cannot be randomly added in any succeeding run? And you wan't the 2nd listbox to be cleared from all items on each run?

So the first listbox is sort of a deck of cards and the run deals a hand (of user-defined size) to the 2nd listbox. On any following run the cards on the hand are discarded and a new hand is dealt from the limited number of cards left.

Am I right in my assumptions?

[irishlad]

lol sort of. I work in a prison. The user will populate the first listbox with cells for their particular unit (beds can be added and deleted at any time) and is saved to a text file. When the user loads the program the first listbox will load with the cells that have been added (but I don't want this to be edited unless they so choose to, ie removed from the listbox with the "'lbxData.Items.RemoveAt(randomNumber)" because if they save again they will loose the info). There can be upward of 1200 cells. They will randomly choose, say 100, cells to be selected for searches or urinaylisis testing. I want that list populated in the second listbox, but not remove any of the items in the first listbox. Hope this makes it more clear

[ThomasJohnsen]

lol sort of. I work in a prison. The user will populate the first listbox with cells for their particular unit (beds can be added and deleted at any time) and is saved to a text file. When the user loads the program the first listbox will load with the cells that have been added (but I don't want this to be edited unless they so choose to, ie removed from the listbox with the "'lbxData.Items.RemoveAt(randomNumber)" because if they save again they will loose the info). There can be upward of 1200 cells. They will randomly choose, say 100, cells to be selected for searches or urinaylisis testing. I want that list populated in the second listbox, but not remove any of the items in the first listbox. Hope this makes it more clear

Ok - think I have a clearer understanding of the problem now. Cells will never be removed by the random picks to testing. Cells can be added or removed by other sources not discussed here. Would it be sensible to add some sort of tag ('last checked on date' or similar) to the currently selected cells for analysis, and not allow any cell that has been checked within a specified timeframe to be selected for analysis?

[dbasnett]

    Dim PRNG As New System.Random 'note - declared in namespace

    Private Sub Button1_Click(sender As System.Object, _
                              e As System.EventArgs) Handles Button1.Click

        lbxRandom.Items.Clear()

        Dim count As Integer
        Dim tl As New List(Of Integer)

        'textbox for user to choose the number of randomly generated items
        If Integer.TryParse(tbxRandom.Text, count) Then
            For x As Integer = 1 To count
                Dim idx As Integer
                If lbxRandom.Items.Count = lbxData.Items.Count Then
                    'error
                    Stop
                End If
                Do
                    idx = PRNG.Next(lbxData.Items.Count)
                Loop While tl.Contains(idx)
                tl.Add(idx)
                lbxRandom.Items.Add(lbxData.Items(idx))
            Next
        Else
            MessageBox.Show("Problem with that number you entered")
        End If
    End Sub

[irishlad]

TJ thanks for all the help. No I think that is a bit overkill as this list will only be generated once a month and won't matter who was randomly chosen in the past. dbasnett's code works great too, only it still removes the selections from the lbxdata listbox. If I can get suggestions to tweak his/her code to send the lbxdata to an array and then randomly choose from the array where it won't matter if the items are removed after selection and placed in the lbxRandom listbox, I think is what i'm looking for.

[irishlad]

Arrrggg. Never mind, forgot to do something. dbasnett's code is exactly was I was looking for. Thanks again for the help guys!!!!!!