如何在vb.net中使用字典dataype

Question

I am facing problems with this code, Can anyone suggest what are the problems with it, I am trying to find the frequency of each element in an array

 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

Here's your code little bit refactored:

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

This loop:

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

is unnecessary, in outer loop we will count occurences (anyway, this way you might determine frequency, but you don't use it anyway, also you are counting it for every item separately, which is very, very inefficient).

The problem with your dictionary was, that you weren't adding any elements to it! Your if statement should look like:

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