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Random Sort

Posted on 2004-04-25
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Last Modified: 2012-05-11
I need to randomly sort a 70 part array.
I have something written now, but it is very slow.
This is how my process works.
Start a loop for 70 items.
Generate a random number between 0 and 69.
Compare that to the numbers already generated.
If the match is found, generate another new number and re-compare against list.
If there is no match found, add the new number to the array and loop until we hit 70 items.
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Question by:TeleKawaru
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14 Comments
 
LVL 15

Expert Comment

by:unknown_routine
ID: 10915640
how do you mean by very slow? how long it takes?


array of numbers or strings?
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Author Comment

by:TeleKawaru
ID: 10915689
It was a problem with my logic actually. I got it figured out.
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LVL 53

Expert Comment

by:Dhaest
ID: 10915694
A very quick sub to perform it.
The trick to make it quick is using a dynamic table, where we change the size of the loop when it's bigger.

Dim intArray() As Integer

Private Sub DoRandomNumber()
    Dim bSame As Boolean
    For i = 0 To 69
        myrandom = Int((70 * Rnd) + 1)
        ReDim Preserve intArray(i)
        bSame = False
        For j = 0 To UBound(intArray)
            If intArray(j) = myrandom Then bSame = True
        Next j
        If bSame = False Then
            intArray(i) = myrandom
        Else
            i = i - 1
        End If
    Next i
End Sub

Private Sub Command1_Click()
    DoRandomNumber
End Sub
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LVL 11

Expert Comment

by:dbrckovi
ID: 10916103
Try this:

It algorythm will loop X times for an array of X elements (not more). In this particular case it will loop 70 times.

It doesn't generate a number for each position. It genereates a position for each number.

Theory:

Place 70 positions (addresses into a listboX)
- get first number
- get a random entry from this list
- put the first number to this adress
- remove that address from a listbox (so we won't get it again)

- get second number
- get another random entry from listbox (since we have removed an adreess of the first number, this will return an unique adress)
- put second number to this position
- remove that adress
     .
     .
     .

Here's the code:
- Put comand button and two listboxes on a form
- Names of the listboxes:     HelpList      and        ResultList

--------------------------------------------------------------------------
Dim MainArray(0 To 69) As Integer
Dim RandomizedArray(0 To 69) As Integer

Private Sub Command1_Click()
    Dim WhereToPut As Integer
    Dim HelpIndex As Integer
    Dim Number As Integer
   
    Randomize Timer
    For x = 0 To 69                 'Fill Listbox with numbers (positions)
        HelpList.AddItem x
    Next x
   
    For x = 0 To 69                 'Randomize position for each number (70 times, not more)
        Number = MainArray(x)                                   'get a number for which we are randomising position
        HelpIndex = Int(Rnd * (HelpList.ListCount - 1))         'get random entry from listbox
        WhereToPut = HelpList.List(HelpIndex)                   'get the number that is under this entry (it is our new position)
        RandomizedArray(WhereToPut) = Number                    'put a number into new array to new position
        HelpList.RemoveItem (HelpIndex)                         'remove this entry. This ensures that we won't try to put two numbers to the same position
    Next x

    For x = 0 To 69
        ResultList.AddItem RandomizedArray(x)                   'Display the results
    Next x
End Sub

Private Sub Form_Load()
    HelpList.Visible = False
    For x = 0 To 69
        MainArray(x) = x                    'fill main array with numbers
    Next x
End Sub
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LVL 11

Expert Comment

by:dbrckovi
ID: 10916236
This is better version of the above algorythm.
It can randomize any array of any type, but number of elements must not be larger that 32767 becouse this is the listbox limit (integer)
LBound doesn't have to start from 0.

----------------------------------------------------------------------------------
Private Sub Command1_Click()
    Dim MainArray(48 To 61) As String
   
    For x = 48 To 61
        MainArray(x) = Chr(x)
    Next x
   
    RandomizeArray MainArray

    ResultList.Clear
    For x = 48 To 61
        ResultList.AddItem MainArray(x)
    Next x
End Sub

Private Sub Form_Load()
    HelpList.Visible = False
End Sub

Sub RandomizeArray(ByRef ArrayToSort As Variant)
    Dim WhereToPut As Integer
    Dim HelpIndex As Integer
    Dim Value As Variant
    Dim RandomizedArray() As Variant
   
    ReDim RandomizedArray(LBound(ArrayToSort) To UBound(ArrayToSort))
    Randomize Timer
    HelpList.Clear
    For x = LBound(ArrayToSort) To UBound(ArrayToSort)                  'Fill Listbox with numbers (positions)
        HelpList.AddItem x
    Next x
   
    For x = LBound(ArrayToSort) To UBound(ArrayToSort)                 'Randomize position for each number (70 times, not more)
        Value = ArrayToSort(x)                                   'get a number for which we are randomising position
        HelpIndex = Int(Rnd * (HelpList.ListCount))          'get random entry from listbox
        WhereToPut = HelpList.List(HelpIndex)                   'get the number that is under this entry (it is our new position)
        RandomizedArray(WhereToPut) = Value                    'put this number into new array
        HelpList.RemoveItem (HelpIndex)                         'remove this entry. This ensures that we won't try to put two numbers to the same position
    Next x

    For x = LBound(ArrayToSort) To UBound(ArrayToSort)
        ArrayToSort(x) = RandomizedArray(x)
    Next x
End Sub
----------------------------------------------------------------------
To use it in your existing project, just paste RandomizeArray sub and create a HelpList listbox.
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LVL 26

Expert Comment

by:EDDYKT
ID: 10917601
Use collection to identify whether the number is generated
So you don't have to loop through your own list

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LVL 26

Expert Comment

by:EDDYKT
ID: 10917627
ie

Option Explicit
Dim col As New Collection


Private Sub Form_Load()
Dim tmp As Integer

On Error Resume Next
Do Until col.Count = 70
    tmp = Int((70 * Rnd) + 1)
    col.Add tmp, CStr(tmp)
Loop
End Sub
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LVL 44

Expert Comment

by:Arthur_Wood
ID: 10917833
actually, a much better appraoch to this problem is to look at it for what it REALLY is, a SHUFFLE (think of suffleing a DECK of 70 cards).

what you want is to have the Numbers from 1 to 70 come up in a random order, with no one number appearing more than once.  That is what shuffling a deck of cards produces.  The set of cards is fixed, it is just the order that needs to be scrambled.

Where the alogorithms that you are proposing begin to bog down is when the number of REAMINIG values to be generated becomes SMALL (sy you have generated 65 of the 70 values, so only 5 more can be set.  But it takes longer to have the Random number genrator actually generate one of those 5 values, and when only two values remain, it takes even longer).

With a Shuffle algorithm, it takes 7 or 8 passes through the array, to completely shuffle the arrsy into a truly random order.  Once the array has beenshuffled, then it is a simple matter to step through the arrsy, on value at a time, retriving each RANDOM value.

here is some code to accomplish exactly this:

Dim deck(1 To 70) As Integer 'the array which holds the cards
'the following are just a few counters
Dim n As Integer
Dim temp As Integer
Dim i As Integer
Dim temp1 As Integer
'this statement is used to return differ
'     ent random numbers each time we run the
'     application
Randomize Timer
'the following loop assigns the numbers
'     1 to 70 to the array in that order.


For n = 1 To 70
    deck(n) = n
Next n
'time to do the shuffling


For i = 0 To 9'this llop just repeats the shuffling process 10 times


    For temp = 1 To 70
        n = Int((70 * Rnd) + 1) this generates a random number in the range 1 To 70
        'the following block of code interchange
        '     s the values of deck(temp) & deck(n). Th
        '     is is a very simple method of shuffling
        '     the array. If you read it carefully you
        '     will be able to understabd the logic.
        temp1 = deck(temp)
        deck(temp) = deck(n)
        deck(n) = temp1
    Next temp
Next i

AW
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LVL 11

Expert Comment

by:dbrckovi
ID: 11257734
Since TeleKawaru said they figured it out on their own, a refund is considerable, but on the other hand we gave at least 3-4 working sollutions, and since TeleKawaru
didn't bother to close the question, I assume they don't care about the points, but I'll be free to say that the rest of us do.
So I reccomend a split.

On the yet another hand, maybe TeleKawaru doesn't know how to close the question, in that case I would suggest to wait


In any case I wouldn't delete this question, becouse random sorting and shuffling is a common question on EE, so it might be usefull as a PAQ.
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Author Comment

by:TeleKawaru
ID: 11301942
Hello,

I tried to close the question once I figured out that it was my mistake, but by that time, someone had already posted something so I could not close this question. I was unsure as to what to do by that point, which is why I just posted that I had figured it out. Not sure why so many people gave answers after I had already stated that I solved it myself.

If people would think it is unfair for me to just get a refund, I am willing to split the points, but I would not want to be the one to determine the splitting.
0
 
LVL 44

Expert Comment

by:Arthur_Wood
ID: 11303193
post a 0 point question to community support, asking that this question be deleted, and the points refunded.  Explain that you figured out the reason for the problem, on your own.

AW
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Accepted Solution

by:
modulo earned 0 total points
ID: 11358846
Closed, 500 points refunded.

modulo
Community Support Moderator
Experts Exchange
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