Imports System

Imports System.Text.RegularExpressions

Imports System.Linq

Imports System.Collections.Generic

​

Public Module Module1

    Public Sub Main()

        'Include extensions on some of these, to show it works both ways and respects original

        Dim testData = {

            "10_2017.LBK",

            "123_2018",

            "500_2017.lbk",

            "20_2019",

            "100_2017.LbK",

            "25_2017",

            "32_2018"

        }

        'Adapted to use simple strings, since the online repl tool won't like files

        Dim exp As New Regex("(\d{1,3})_(\d{4})")

        Dim f1 As List(Of String) = testData.OrderBy(

            Function(fi) 

                Dim parts = exp.Matches(fi)(0).Groups

                Return (Integer.Parse(parts(2).Value) * 1000) + Integer.Parse(parts(1).Value)

            End Function).

            ToList()

        For Each item As String in f1

            Console.WriteLine(item)

        Next    

    End Sub

End Module