CODEWITHSUNDEEP
vb.netfor-looprandomarraylistshuffle
Novastorm
Novastorm

Reputation: 1458

Random shuffling of elements in an array between 2 indexes VB.NET

I'm trying to shuffle elements between a certain number of indexes. 

Dim rng As New Random()
For placeHolder As Integer = min To max Step -1
            Dim swapIndex As Integer = rng.Next(min, max)
            Dim temp As Object = myList(placeHolder)
            myList(placeHolder) = myList(swapIndex)
            myList(swapIndex) = temp
Next

Where 'min' is the value of the lowest index and 'max' is the value of the highest index. However each time I have tried it doesn't seem to be shuffling randomly (it always comes out alphabetically instead).

Upvotes: 0

Views: 149

Answers (2)

Arkain
Arkain

Reputation: 938

Try this:

Dim rng As New Random()
For placeHolder as Integer = min To max-1 Step 1
   Dim swapIndex as Integer = rng.Next(placeHolder +1, max)
   Dim temp as Object = myList(placeHolder)
   myList(placeHolder) = myList(swapIndex)
   myList(swapIndex) = temp
Next

The changes? I changed the max value being stepped over to 1 less than the end so that you don't waste time trying to swap the end with itself. I also changed the Step to +1 because min < max from your description. I changed the minimum random value to placeholder + 1 because I don't want to re-swap what I've already swapped. This last change is optional though.

Upvotes: 1

Ross Presser
Ross Presser

Reputation: 6255

if min is the lowest and max is the highest, then your loop should not have Step -1 in it. That will cause the loop to never execute.

Upvotes: 0

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