shuffling or randomizing a set of numbers.....

[nynamyna]

Hi everybody

I have a set of nuumbers in a table in the access database. I just want to know how to shuffle those values randomly. Each time if I shuffle then the order of the numbers should be randomized. I know how to sort them in ascending and descending...but I don't know how to shuffle them....please help me.....

Thanks
Bharath

 

[picoflop]

Check this:
Fisher–Yates shuffle - Wikipedia, the free encyclopedia

 

[MattP]

Couple of examples using a Shuffle(Of T) function and using LINQ to achieve the results.

Public Class Form1

    Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
        'Using shuffle function
        Dim fruit As New List(Of String)
        fruit.AddRange(New String() {"Apple", "Banana", "Grape", "Orange", "Tomato"})
        fruit = Shuffle(Of String)(fruit.ToArray).ToList

        Dim ints As New List(Of Integer)
        ints.AddRange(New Integer() {1, 2, 3, 4, 5})
        ints = Shuffle(Of Integer)(ints.ToArray).ToList

        'Using lambda
        Dim fruit2 As New List(Of String)
        fruit2.AddRange(New String() {"Apple", "Banana", "Grape", "Orange", "Tomato"})
        Dim rnd As New Random()
        fruit2 = fruit2.OrderBy(Function() rnd.Next).ToList

        'Full LINQ syntax example
        Dim fruit3 As New List(Of String)
        fruit3.AddRange(New String() {"Apple", "Banana", "Grape", "Orange", "Tomato"})
        fruit3 = (From f In fruit3
                 Order By rnd.Next
                 Select f).ToList
    End Sub

    Private Shared Function Shuffle(Of T)(ByVal OriginalArray As T()) As T()
        Dim matrix = New SortedList()
        Dim r = New Random()

        For x = 0 To OriginalArray.Length - 1
            Dim i = r.Next()

            While matrix.ContainsKey(i)
                i = r.Next()
            End While

            matrix.Add(i, OriginalArray(x))
        Next

        Dim OutputArray = New T(OriginalArray.Length - 1) {}

        matrix.Values.CopyTo(OutputArray, 0)

        Return OutputArray
    End Function

End Class

 

[picoflop]

@MattP: If your array is large, your function will run very long I assume (bc it selects a random number and checks if it was already selected). Fisher-Yates has a complexity of O, while yours is much worse for large n.

 

[MattP]

You're correct in that it would run slower for large sets of data. Rewrote it to use something more reasonable for large values of n.

        Dim fruit As New List(Of String)
        fruit.AddRange(New String() {"Apple", "Banana", "Grape", "Orange", "Tomato"})
        ShuffleMe(Of String)(fruit)

    Public Shared Sub ShuffleMe(Of T)(ByRef TheList As List(Of T))
        Dim rnd As New System.Random
        Dim tmpArray() As T = TheList.ToArray
        Dim len As Integer = tmpArray.Length
        While (len > 1)
            Dim idx As Integer = rnd.Next(len)
            len -= 1
            Dim temp As T = tmpArray(len)
            tmpArray(len) = tmpArray(idx)
            tmpArray(idx) = temp
        End While
        TheList = tmpArray.ToList
    End Sub

 

[nynamyna]

thanks for your help.....I did it with your code....

Bharath