How to check a random value and avoid for the same random value?

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Hello all.
I've asking this, but I've try some solution and it still won't work :(
My problem is, when I generate a random, there's many same random value shown.
And I've improve my code for check them one by one, if the random value same, then the value have to randomed again, and it was not work :(

Here's my code :

VB

For i = 1 To PopuMain.members_count
            For j = 1 To PopuMain.GenoLength
                PopuMain.Members(i).Genome(j) = Rand_between(1, 513)
                If j > 1 Then
                    For k = 1 To j - 1
                        If PopuMain.Members(i).Genome(j) = PopuMain.Members(i).Genome(k) Then
                            PopuMain.Members(i).Genome(j) = Rand_between(1, 513)
                        End If
                    Next
                End If
            Next j

And this the random function :

VB

Public Function Rand_between(ByRef Minimum As Integer, ByRef Maximum As Integer) As Double
        Randomize()
        Rand_between = Int((Maximum - Minimum + 1) * Rnd() + Minimum)
    End Function

Please give me a solution(Check my code) for this one :(
Thanks a lot for your help :)

Sorry my english bad, I'm an indonesian :)

Posted 13-May-11 2:19am

Abdi tombang

Updated 13-May-11 2:27am

Nithin Sundar

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#realJSOP · Accepted Answer · 2011-05-13T02:42:00

Createa HashSet, and like griff said, preload it with say, 10 random numbers. Since Hashsets don't allow duplicates, this will guarantee 10 unique random numbers.

Put your random number generator into a thread, so it can work behind the scenes (adding items to a hashset can negatively impact performance as the list gets longer and longer). If you establishg a threshhold where repeating randoms don't matter, you can trigger the hashset to be reduced by a given number of entries after adding a new batch of random values.

So, if you establish that numbers have to be different from the most previous 100 random values, you simply maintain a hashset collection that is never larger than 100 items.

#realJSOP · Accepted Answer · 2011-05-13T04:36:00

Create a class tha looks something like this:

C#

public class RandomValuesHash : HashSet<int>
{
    public int MaxCount { get; set; }
    public int MinValue { get; set; }
    public int MaxValue { get; set; }
    public int MinDelta { get; set; }

    private Random random = new Random(DateTime.Now.Milliseconds);

    public RandomValuesHash()
    {
        // reasonable defaults
        this.MaxCount = 100;
        this.MinValue = 1;
        this.MaxValue = 200;
        this.MinDelta = 90; // when the count drops to 90, top the list off
        // populate the collection
        AddValues();
    }

    public void AddValues()
    {
        if (this.Count <= this.MinDelta)
        {
            // now top-off the collection
            while (this.Count < MAX_COUNT)
            {
                this.Add(random.Next(this.MinValue, this.MaxValue));
            }
        }
    }

    public void RemoveItem(int index)
    {
        this.RemoveAt(index, 1);
    }

    public int GetNextValue()
    {
        int value = this[0];
        RemoveItem(0);
        AddValues();
        return value;
    }
}

The class above takes care of all the details, so all you have to do is instantiate when the app starts, and then start retrieving values from it. The list maintains itself.

C#

RandomValuesHash randomSet = new RandomValuesHash() { set your properties here if ou want something other than the defaults };

int newRandomValue = randomSet.GetNextValue();

To be brutally honest, when I gave you the description of what you needed to do, you shouldhave been able to do it (or figure it out on your own. Part of being a programmer is being able to analyze and design a solution as well as implement it. The implementation (writing the code) is the easy part, especially if the analysis and design have been done beforehand.

OriginalGriff · Accepted Answer · 2011-05-13T02:33:00

Solution 1

Rule one: Don't do Randomize repeatedly: it encourages duplicates as it uses the system clock as a seed.

Call it once, outside all your loops and it should improve things.

The other thing is the nature of random numbers: they are random. That means that every number in the phase space has an equal chance of being the next number drawn: it does not rely (or even check) if a random number has been drawn already.

If you seriously want all different random numbers, then generate an array or a List of random numbers before you enter the loops, and remove all duplicates when you load it.

Posted 13-May-11 2:33am

OriginalGriff

Comments

Abdi tombang 13-May-11 8:49am

"If you seriously want all different random numbers, then generate an array or a List of random numbers before you enter the loops, and remove all duplicates when you load it."

Really good idea, I try for this one, but still can't make the code :(
Whice part of my code should improved for apply this one??

OriginalGriff 13-May-11 8:52am

See JSOP's reply - It's a good idea!

Abdi tombang 13-May-11 8:56am

I've his briliant idea.
But I'm still confuse how to implement his ide into my code :(
Whice part of my code should improved for apply this one??

Sergey Alexandrovich Kryukov 13-May-11 14:07pm

All correct, but removing all duplicates would be really ugly. Duplicated should not be added, like it's done with hash sets and dictionaries. So, my 4 this time.
--SA

How to check a random value and avoid for the same random value?

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