一种打印无数内容的有效方法 [英] Efficient method to print the content of an Ienumerable

问题描述

我有一个结果"变量，它是IEnumerable类型:

I have this "result" var which is a IEnumerable type:

Dim result = GetCombinations(TextBox1.Text, StringLength)

要获取/写入变量的内容，我需要使用For来迭代内部的所有项目，然后将每个项目转换为数组，如下所示:

To get/write the content of the variable I need to iterate all the items inside using a For and then convert each item to an array, like this:

    For Each item In result
        RichTextBox1.Text += vbNewLine & item.ToArray
        Application.DoEvents()
    Next

...所以我的答案是，如果我可以改进代码，例如加入IEnumerable内容以执行其他操作:

...So my answer is If I can improve my code for example to join the IEnumerable content to do something like this else:

 RichTextBox1.Text = String.Join(vbNewLine, result) ' This does not work.

我的意思是，一口气".

I mean, a "in one go" thing.

如果没有，是否有其他替代方案比For更好(更快)?

If not, any alternative better (faster) than the For?

更新

这是完整的代码:

Private Shared Function GetCombinations(Of T)(list As IEnumerable(Of T), length As Integer) As IEnumerable(Of IEnumerable(Of T))

    If length = 1 Then
        Return list.[Select](Function(x) New T() {x})
    Else
        Return GetCombinations(list, length - 1).SelectMany(Function(x) list, Function(t1, t2) t1.Concat(New T() {t2}))
    End If

End Function

   Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click

    RichTextBox1.Clear()

    Dim result = GetCombinations("abc", 5)

    ' Dim result2 As IEnumerable(Of String) = result.Select(Function(item) New String(item))

    ' RichTextBox1.Text = String.Join(vbNewLine, result)

    For Each item In result
        RichTextBox1.Text &= vbNewLine & item.ToArray
        '  Application.DoEvents()
    Next

End Sub

更新2

Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click

    ' Method result
    Dim result As IEnumerable = Permute_Characters("abc", 2)

    ' Combine strings into lines
    ' Dont work
    RichTextBox1.Text = String.Join(Environment.NewLine, result.ToString.ToArray)

End Sub

推荐答案

如果要提高速度并减少内存占用，请减少递归和对LINQ的调用(这会隐藏内部循环).

If you want speed and reduced memory footprint, then reduce the recursions and calls to LINQ (which hide internal loops).

现在我已经了解了您想要的内容，请尝试以下代码

Now that I understand what you want, try this code

Public Function GetCombinations(ByVal letters As String, ByVal word_length As Integer) As String()
    ' abc,2 -> aa, ab, ac, ba, bb, bc, ca, cb, cc
    ' abc,3 -> aaa, aab, aac, aba, abb, abc, .. , caa, cab, cac
    Dim list = letters.ToCharArray()
    Dim N_letters = list.Length
    Dim N_combinations = CLng(Math.Pow(N_letters, word_length))
    Dim result As New List(Of String)(N_combinations)
    ' indeces holds which letter to use for each combination
    ' 0 = a, 1 = b, 2 = c, ...
    ' it starts with (0,0,0..) which corresponds to "aaa.."
    Dim indeces As Integer() = New Integer(word_length-1) {}
    'Default to 0's
    Dim k As Integer
    Do
        ' convert indeces into combination, example: (1,0,2) => (b,a,c) => "bac"
        result.Add(New String(indeces.Select(Function(x) list(x)).ToArray()))
        'Find next combination by incrementing the first letter,
        'and if it spills-over, reset it to 'a' and try the next letter in the word
        k = 0
        Do
            indeces(k) += 1

            If indeces(k) = N_letters Then
                indeces(k) = 0
                k = k + 1
            Else
                Exit Do
            End If
        Loop While k < word_length
    Loop While k < word_length

    Return result.ToArray()

End Function


Sub Main()
    Dim result = GetCombinations("abc", 5)
    Debug.WriteLine(String.Join(ControlChars.CrLf, result))
End Sub

有结果

aaaaa
baaaa
caaaa
abaaa
bbaaa
cbaaa
acaaa
bcaaa
ccaaa
aabaa
babaa
...
caccc
abccc
bbccc
cbccc
acccc
bcccc
ccccc

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