如何在vb.net中使用字典dataype

Question

我正面临这段代码的问题，谁能建议它有什么问题，我试图找到数组中每个元素的频率

 Public Sub P3()
    Dim no, freq, arr(5) As Integer
    Dim dict As New Dictionary(Of Integer, Integer)()
    Console.WriteLine("Enter 5 Integer Elements : ")
    For i = 0 To 4
        arr(i) = Console.ReadLine()
    Next
    For i = 0 To 4
        no = arr(i)
        For j = 0 To 4
            If no = arr(i) Then
                freq += 1
            End If
        Next
        If dict.ContainsKey(no) Then
            dict(i) += 1
        End If
        freq = 0
    Next

    For Each ab As KeyValuePair(Of Integer, Integer) In dict
        Console.WriteLine("Frequency Of " & ab.Key, " is " & ab.Value)
    Next
End Sub

Answer 1

这是您稍微重构的代码：

Public Sub P3()
    Dim no, arr(5) As Integer
    Dim dict As New Dictionary(Of Integer, Integer)()
    Console.WriteLine("Enter 5 Integer Elements : ")
    For i = 0 To 4
        arr(i) = Console.ReadLine()
    Next
    For i = 0 To 4
        no = arr(i)
        If dict.ContainsKey(no) Then
            dict(no) += 1
        Else
            dict.Add(no, 1)
        End If
    Next

    For Each ab As KeyValuePair(Of Integer, Integer) In dict
        Console.WriteLine("Frequency Of " & ab.Key & " is " & ab.Value)
    Next
End Sub

这个循环：

For j = 0 To 4
    If no = arr(i) Then
        freq += 1
     End If
Next

是不必要的，在外循环中我们将计算出现次数（无论如何，通过这种方式您可以确定频率，但无论如何您都不会使用它，而且您还单独为每个项目计算它，这是非常非常低效的）。

你的字典的问题是，你没有向它添加任何元素！ 您的 if 语句应如下所示：

If dict.ContainsKey(no) Then
    dict(no) += 1
Else
    dict.Add(no, 1)
End If

Answer 2

Private Sub TestDic()
    Dim dic As New Dictionary(Of Integer, Integer) From
    {
        {1, 100},
        {2, 200},
        {3, 100},
        {4, 70},
        {5, 200},
        {6, 300}
    }
    Dim z = dic.GroupBy(Function(k) k.Value).
            Select(Function(w) New With {.Value = w.Key, .Count = w.Count()})
    '// Dump results to ListBox
    z.ToList().ForEach(Sub(x) lstResults.Items.Add($"Value: {x.Value}, Count = {x.Count}"))
End Sub