Получить значение элемента, который встречается чаще всего в данном массиве

Если тебе надо отсортировать массив, то перебрось всё его содержимое в ListBox (с заранее установленным Sorted=True), а потом обратно

    Private Class FullAnalizer
        Dim a_date() As DateTime
        Dim a_count() As Integer
        Dim is_over As Boolean
        Dim rez_date As DateTime

        Public Function GetDate(ByVal filename As String) As DateTime
            ReDim a_date(-1)
            ReDim a_count(-1)
            is_over = False
            Dim foo As New clsUniverseParser
            AddHandler foo.GotSubrevPacket, AddressOf SubrevPacket
            AddHandler foo.GotRevshPacket, AddressOf RevshPacket
            Try
                foo.ParseUnknown(filename)
            Catch ex As clsSubrev.SubrevParserException
                If is_over Then
                    Return rez_date
                Else
                    Throw ex
                End If
            Catch ex As clsRevsh.RevshParserException
                If is_over Then
                    Return rez_date
                Else
                    Throw ex
                End If
            Catch ex As Exception
                Throw ex
            End Try
            If is_over Then
                Return rez_date
            Else
                Throw New Exception("Полный анализ завершился, но дата не определена!"
            End If
        End Function
        Private Sub SubrevPacket(ByVal sender As Object, ByVal in_array() As clsSubrev.typeSubrev, ByVal Count As Integer)
            If (Not is_over) Then
                Dim f As Integer
                Dim i As Integer
                For i = 0 To Count - 1
                    f = Array.IndexOf(a_date, in_array(i).dt_charge.Date)
                    If f = -1 Then
                        Dim max As Integer = a_date.Length
                        ReDim Preserve a_date(max)
                        ReDim Preserve a_count(max)
                        a_date(max) = in_array(i).dt_charge.Date
                        a_count(max) = 1
                    Else
                        a_count(f) += 1
                    End If
                Next
                CalculateDate()
                If is_over Then
                    CType(sender, clsUniverseParser).StopParsing()
                End If
            End If
        End Sub
        Private Sub CalculateDate()
            Dim rez_indx As Integer = -1
            Dim low, hi, i As Integer
            For i = 0 To a_count.Length - 1
                If a_count(i) < a_count(low) Then
                    low = i
                End If
                If a_count(i) > a_count(hi) Then
                    hi = i
                End If
            Next
            If a_count(hi) > 1000 Then
                If hi <> low Then
                    If a_count(hi) / a_count(low) > 10 Then
                        rez_indx = hi
                    End If
                Else
                    rez_indx = hi
                End If
            End If
            If rez_indx > -1 Then
                is_over = True
                rez_date = a_date(hi)
            End If
        End Sub

        Private Sub RevshPacket(ByVal sender As Object, ByVal in_array() As clsRevsh.typeRevsh, ByVal Count As Integer)
            If (Not is_over) Then
                Dim f As Integer
                Dim i As Integer
                For i = 0 To Count - 1
                    f = Array.IndexOf(a_date, in_array(i).dt_ce.Date)
                    If f = -1 Then
                        Dim max As Integer = a_date.Length
                        ReDim Preserve a_date(max)
                        ReDim Preserve a_count(max)
                        a_date(max) = in_array(i).dt_ce.Date
                        a_count(max) = 1
                    Else
                        a_count(f) += 1
                    End If
                Next
                CalculateDate()
                If is_over Then
                    CType(sender, clsUniverseParser).StopParsing()
                End If
            End If
        End Sub
    End Class