有没有一种简单的方法可以在 VB.NET 中随机化列表? [英] Is there an easy way to randomize a list in VB.NET?

问题描述

我有一个 System.IO.FileInfo 类型的列表，我想随机化这个列表.我想我记得不久前看到过类似 list.randomize() 的东西，但我找不到在哪里看到过.

I have a list of type System.IO.FileInfo, and I would like to randomize the list. I thought I remember seeing something like list.randomize() a little while back but I cannot find where I may have seen that.

我第一次尝试使用这个功能:

My first foray into this yielded me with this function:

Private Shared Sub GetRandom(ByVal oMax As Integer, ByRef currentVals As List(Of Integer))
    Dim oRand As New Random(Now.Millisecond)
    Dim oTemp As Integer = -1
    Do Until currentVals.Count = IMG_COUNT
        oTemp = oRand.Next(1, oMax)
        If Not currentVals.Contains(oTemp) Then currentVals.Add(oTemp)
    Loop
End Sub

我向它发送我希望它迭代到的最大 val，以及对我想要随机化内容的列表的引用.变量 IMG_COUNT 在脚本中设置得更远，指定如何我想显示许多随机图像.

I send it the max val I want it to iterate up to, and a reference to the list I want the randomized content in. The variable IMG_COUNT is set farther up in the script, designating how many random images I want displayed.

谢谢大家，我很感激:D

Thanks guys, I appreciate it :D

推荐答案

构建比较器:

Public Class Randomizer(Of T)
    Implements IComparer(Of T)

    ''// Ensures different instances are sorted in different orders
    Private Shared Salter As New Random() ''// only as random as your seed
    Private Salt As Integer
    Public Sub New()
        Salt = Salter.Next(Integer.MinValue, Integer.MaxValue)
    End Sub

    Private Shared sha As New SHA1CryptoServiceProvider()
    Private Function HashNSalt(ByVal x As Integer) As Integer
      Dim b() As Byte = sha.ComputeHash(BitConverter.GetBytes(x))
      Dim r As Integer = 0
      For i As Integer = 0 To b.Length - 1 Step 4
          r = r Xor BitConverter.ToInt32(b, i)
      Next

      Return r Xor Salt
    End Function

    Public Function Compare(x As T, y As T) As Integer _
        Implements IComparer(Of T).Compare

        Return HashNSalt(x.GetHashCode()).CompareTo(HashNSalt(y.GetHashCode()))
    End Function
End Class

像这样使用它，假设你的意思是一个通用的List(Of FileInfo):

Use it like this, assuming you mean a generic List(Of FileInfo):

list.Sort(New Randomizer(Of IO.FileInfo)())

您也可以使用闭包使随机值粘滞"，然后在其上使用 linq 的 .OrderBy()(这次是 C#，因为 VB lambda 语法很难看):

You can also use a closure to make the random value 'sticky' and then just use linq's .OrderBy() on that (C# this time, because the VB lambda syntax is ugly):

list = list.OrderBy(a => Guid.NewGuid()).ToList();

在这里解释，以及为什么它甚至可能不如真正的洗牌快:
http://www.codinghorror.com/blog/archives/001008.html?r=31644

Explained here, along with why it might not even be as fast as real shuffle:
http://www.codinghorror.com/blog/archives/001008.html?r=31644

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