Question

我不想结合两个字符串列表，它们都有200000多个项目。这是我用来组合它们的代码：

For Each item in list2
   list1.add(item)
Next

但问题是将list2中的每个项目添加到list1需要很长时间。所以我问，是否有更好的解决方案来组合这些列表？

Answer 1

List类中有一个内置方法可以完全满足您的需求：

list1.AddRange(list2)

查看Microsoft页面here以查看其他信息。
无论如何，你真的确定你需要在内存中有这么多的字符串吗？

Answer 2

我也很想知道需要，但如果你需要它们，可以考虑使用StringBuilder。我跑了一点测试：

Private Sub Button1_Click(sender As System.Object, _
                          e As System.EventArgs) Handles Button1.Click
    Dim stpw1 As New Stopwatch
    Dim stpw2 As New Stopwatch

    'sample data
    Dim ipsumA() As String = New String() {"Lorem", "ipsum", "dolor", "sit", _
                                           "amet", "consectetur", "adipisicing", _
                                           "elit", "sed", "do", "eiusmod", _
                                           "tempor", "incididunt", "ut", "labore", _
                                           "et", "dolore", "magna", "aliqua", "Ut", _
                                           "enim", "ad", "minim", "veniam", "quis", _
                                           "nostrud", "exercitation", "ullamco", _
                                           "laboris", "nisi", "ut", "aliquip", "ex", _
                                           "ea", "commodo", "consequat", "Duis", "aute", _
                                           "irure", "dolor", "in", "reprehenderit", "in", _
                                           "voluptate", "velit", "esse", "cillum", "dolore", _
                                           "eu", "fugiat", "nulla", "pariatur", "Excepteur", _
                                           "sint", "occaecat", "cupidatat", "non", "proident", _
                                           "sunt", "in", "culpa", "qui", "officia", "deserunt", _
                                           "mollit", "anim", "id", "est", "laborum"}

    Dim list1 As New List(Of System.Text.StringBuilder)
    Dim list2 As New List(Of System.Text.StringBuilder)
    Debug.WriteLine("Approx. 200,000+ strings per list")
    stpw2.Restart()
    stpw1.Restart()
    Do While list1.Count < 200000
        For Each s As String In ipsumA
            list1.Add(New System.Text.StringBuilder(s))
            list2.Add(New System.Text.StringBuilder(s))
        Next
    Loop
    stpw1.Stop()
    Debug.WriteLine(stpw1.Elapsed.ToString)

    stpw1.Restart()
    list1.AddRange(list2)
    stpw1.Stop()
    stpw2.Stop()

    Debug.WriteLine(stpw1.Elapsed.ToString)
    Debug.WriteLine(stpw2.Elapsed.ToString)
End Sub

花了大约0.3秒，这是值得的。

Answer 3

如果您事先知道列表的近似最大大小，请在构造函数中指定它。 List<T>在内部使用数组来保存项目。如果没有指定尺寸，它的原始尺寸为4个。如果已满，则创建具有double size的新数组，并将旧数组的内容复制到新数组。对于40万件物品，这种情况多次发生！

var list1 = new List<string>(500000);

加快项目添加到列表

3 个答案: