A For Each statement that visits items in random order

At times you may need to process elements of an array, a collection, or a dictionary object in random order, for example when sampling a population or (more often) when writing a game, such as a card game. Here’s a class that you can use in a For Each statement to randomly process all the elements of any data structure that implements the IEnumerable interface:

Class RandomIterator    Implements IEnumerable    ' a low-overhead ArrayList to store references    Dim items As New ArrayList()    Sub New(ByVal collection As IEnumerable, ByVal seed As Integer)        ' load all the items in the ArrayList, but in random order        Dim rand As New Random(seed)        Dim o As Object        For Each o In collection            Items.Insert(Rand.Next(0, Items.Count + 1), o)        Next    End Sub    Public Function GetEnumerator() As System.Collections.IEnumerator _        Implements System.Collections.IEnumerable.GetEnumerator        ' return the enumerator of the inner ArrayList        Return items.GetEnumerator()    End FunctionEnd Class

This code shows how you can use the RandomIterator class to randomly process all the elements in a string array, but you can use it with collection and dictionaries alike:

Dim arr() As String = {"one", "two", "three", "four", "five" }Dim s As String' the sequence you obtain depends on the seed you pass as the 2nd argumentFor Each s In New RandomIterator(arr, 1234)    Console.WriteLine(s)Next

This code produces the following sequence:

threefivetwofourone

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