How to order list of files by file name with number?

Question

I have a bunch of files in a directory that I am trying to get based off their type. Once I have them I would like to order them by file name (there is a number in them and

Answer 1

I'm assuming the file and .txt parts are mutable, and just here as placeholders for file names and types that can vary.

I don't use regular expressions very often, so this may need some work yet, but it's definitely the direction you need to go:

Dim exp As String = "-([0-9]+)[.][^.]*$"
documentPages = Directory.GetFiles(documentPath, "*.txt").OrderBy(Function(p) Integer.Parse(Regex.Matches(p, exp)(0).Groups(1).Value)).ToList()

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Looking again, I see I missed that you are filtering by *.txt files, which can help us narrow the expression:

Dim exp As String = "-([0-9]+)[.]txt$"

Another possible improvement brought by the other answer that includes test data is to allow for whitespace between the - and numerals:

Dim exp As String = "-[ ]*([0-9]+)[.]txt$"

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It's further worth noting that the above will fail if there are text files that don't follow the pattern. We can account for that if needed:

Dim exp As String = "-[ ]*([0-9]+)[.][^.]*$"
Dim docs = Directory.GetFiles(documentPath, "*.txt")
documentPages = docs.OrderBy(
     Function(p) 
            Dim matches As MatchCollection = Regex.Matches(p, exp)
            If matches.Count = 0 OrElse matches(0).Groups.Count < 2 Then Return 0
            Return Integer.Parse(matches(0).Groups(1).Value)
     End Function).ToList()

You could also use Integer.MaxValue as your default option, depending on whether you want those to appear at the beginning or end of the list.