主题：高效随机抽取少量和大量记录的方法

5楼洗牌的方法是错误的，会导致靠前的记录被抽取的概率大，下面这样，前后的机会才均等：

Dim cnt As Integer = DataTables("订单").DataRows.Count
Dim ids(cnt - 1) As Integer
Dim rnd(cnt -1) As Integer
For i As Integer = 0 To cnt -1
    ids(i) = i
    rnd(i) = rand.Next(0,cnt)
Next
array.sort(rnd,ids)
Tables("订单").StopRedraw()
DataTables("订单").ReplaceFor("选择",False)
For i As Integer =  1 To 100 '100为要抽取的行数
    DataTables("订单").DataRows(ids(i-1))("选择") = True
Next
Tables("订单").Filter = "[选择] = True"
Tables("订单").ResumeRedraw()

但是Array.Sort帮助没有介绍，下面的代码完全采用帮助的知识，性能基本一致：

Dim cnt As Integer = DataTables("订单").DataRows.Count
Dim ids As New List(of Integer)
For i As Integer = 0 To cnt -1
    ids.add(i)
Next
Do
    Dim n As Integer = rand.Next(0,ids.count)
    ids.RemoveAt(n)
Loop While ids.count > 100  '100为要随机抽取的行数
Tables("订单").StopRedraw()
DataTables("订单").ReplaceFor("选择",False)
For Each i As Integer In ids
    DataTables("订单").DataRows(i)("选择") = True
Next
Tables("订单").Filter = "[选择] = True"
Tables("订单").ResumeRedraw()