VB.net choose multiple random items from arraylist only once - vb.net

Question

So I'm trying to make a function where I can input a arraylist and the function randomly picks X amount of items from that arraylist and outputs the result to a new arraylist. This I've got working, the problem I'm having is that after one of the items is picked by the randomize, it's still there which means that it can be picked again. Here is the code I got so far
Dim RandomGeneratorMulti As New ArrayList()
Dim resultMulti As New ArrayList()
RandomGeneratorMulti.Add("Happy")
RandomGeneratorMulti.Add("Sad")
RandomGeneratorMulti.Add("Smart")
RandomGeneratorMulti.Add("Intelegt")
RandomGeneratorMulti.Add("Stupid")
RandomGeneratorMulti.Add("Ugly")
ChooseMulti("5", RandomGeneratorMulti)
TraitsListBox.Items.AddRange(resultMulti.ToArray)
Here is the function
Function ChooseMulti(ByVal Numbers As Integer, ByVal Alist As ArrayList) As ArrayList
Dim rnd = New Random()
For i As Integer = 1 To Numbers
resultMulti.Add(Alist.Item(rnd.Next(0, Alist.Count)))
Next
Return resultMulti
End Function
All help is much appreciated :)

Answer 1

You should use a List(Of String) rather than an ArrayList, but I have written the code below using ArrayList so that it's closer to the original.
You can remove the items that you pick from the list:
Function ChooseMulti(ByVal numbers As Integer, ByVal Alist As ArrayList) As ArrayList
Dim resultMulti As New ArrayList()
Dim rnd = New Random()
For i As Integer = 1 To numbers
Dim index As Integer = rnd.Next(Alist.Count)
resultMulti.Add(Alist.Item(index))
Alist.RemoveAt(index)
Next
Return resultMulti
End Function
Note: As you are returning the list from the function, you should get the return value and put in the resultMulti variable, and not change the variable from inside the function:
resultMulti = ChooseMulti(5, RandomGeneratorMulti)
Another method is to shuffle the list (using Fisher-Yates shuffle) and then take the first items:
Function ChooseMulti(ByVal numbers As Integer, ByVal Alist As ArrayList) As ArrayList
Dim resultMulti As New ArrayList()
Dim rnd = New Random()
For i As Integer = Alist.Count - 1 to 1 Step -1
Dim index = rnd.Next(i + 1)
Dim temp As String = Alist(i)
Alist(i) = Alist(index)
Alist(index) = temp
Next
For i As Integer = 0 To numbers - 1
resultMulti.Add(Alist.Item(i))
Next
Return resultMulti
End Function
Yet another approach is to pick numbers from the list from start to end. That way there can't be duplicates and the original list is left unchanged, but a side effect is that the picked items have the same order as in the original list:
Function ChooseMulti(ByVal numbers As Integer, ByVal Alist As ArrayList) As ArrayList
Dim resultMulti As New ArrayList()
Dim rnd = New Random()
Dim index As Integer = 0
While numbers > 0
If rnd.Next(Alist.Count - index) < numbers Then
resultMulti.Add(Alist.Item(index))
numbers -= 1
EndIf
index += 1
Wend
Return resultMulti
End Function