Randomly Shuffle the Contents of an Array

Category:

Lists, Collections and Arrays

Type:

Snippets

Difficulty:

Intermediate

Author:

Intelligent Solutions Inc.

Version Compatibility:

More information:

This snippet demonstrates a way to randomly shuffle the contents of an array. Though an integer array is used, you can use the same technique for an array of any type.

Instructions: Copy the declarations and code below and paste directly into your VB project.

Declarations:
' (None)

Code:

'PURPOSE OF CODE:

'TO RANDOMLY SHUFFLE CONTENTS OF AN ARRAY

'Array Type and size does not matter
'same technique can be used for arrays of different sizes/types

Dim iArray(200) As Integer 'array to be randomly shuffled
                           'for demo purposes only
Dim iTempArray(200) As Integer 'copy of the array
         
Dim iCtr As Integer
Dim iCtr2 As Integer
Dim iTemp As Integer
Dim iMaxElement As Integer
Dim iMinElement As Integer

'Populate array and Temp Copy for
'demo purposes
For iCtr = 0 To 200
    iArray(iCtr) = iCtr
    iTempArray(iCtr) = iCtr
Next

'iTempArray is an array to hold
'original values. you must duplicate the orignal
'array for this technique to work

'this is the technique
Dim bArray() As Boolean
iMaxElement = UBound(iArray)
iMinElement = LBound(iArray)

ReDim bArray(iMinElement To iMaxElement) As Boolean

For iCtr = iMinElement To iMaxElement
    Do
    Randomize Timer
    iTemp = Int((iMaxElement - iMinElement + 1) * Rnd) + _
        iMinElement
 
        If bArray(iTemp) = False Then
            iArray(iTemp) = iTempArray(iCtr)
            bArray(iTemp) = True
            Exit Do
        End If
    Loop
Next

'just a test to prove that it worked
For iCtr = iMinElement To iMaxElement
    Debug.Print iArray(iCtr)
Next