How to sort numbered filenames in list in C#

Question

I try to sort a list that contains filepaths. And I want them to be sorted by the numbers in them.

With the given code I use I don't get the expected result.

var mylist = mylist.OrderBy(x => int.Parse(Regex.Replace(x, "[^0-9]+", "0"))).ToList<string>();

I expect the result to be:

c:\somedir\1.jpg
c:\somedir\2.jpg
c:\somedir\3.jpg
c:\somedir\7.jpg
c:\somedir\8.jpg
c:\somedir\9.jpg
c:\somedir\10.jpg
c:\somedir\12.jpg
c:\somedir\20.jpg

But the output is random.

Please [edit] your question to include a [mcve], which can be compiled and tested by others. It must have the `Main()` method as an entry point. — Progman, Jun 16 '19 at 18:31
Possible duplicate of [Natural Sort Order in C#](https://stackoverflow.com/questions/248603/natural-sort-order-in-c-sharp) — Dour High Arch, Jun 16 '19 at 18:40
This works for me, apart from the redefinition of the variable. — R.J. Dunnill, Jun 16 '19 at 18:51

Just Shadow · Accepted Answer · 2019-06-16T18:55:20.067

4

There is a simple way of achieving that. Let's say you have a string list like this:

List<string> allThePaths = new List<string>()
{
    "c:\\somedir\\1.jpg",
    "c:\\somedir\\2.jpg",
    "c:\\somedir\\20.jpg",
    "c:\\somedir\\7.jpg",
    "c:\\somedir\\12.jpg",
    "c:\\somedir\\8.jpg",
    "c:\\somedir\\9.jpg",
    "c:\\somedir\\3.jpg",
    "c:\\somedir\\10.jpg"
};

You can get the desired result with this:

List<string> sortedPaths = allThePaths
    .OrderBy(stringItem => stringItem.Length)
    .ThenBy(stringItem => stringItem).ToList();

Note: Also make sure you've included LINQ:

using System.Linq;

Here is a demo example just in case it's needed.

More complex solutions can be found there.

edited Jun 16 '19 at 18:55

answered Jun 16 '19 at 18:40

Just Shadow

10,860
6
57
75

1

In this case `8.jpg` will come before `01.jpg`. may work here but in general there is a chance to fail. – roozbeh S Jun 16 '19 at 18:52
1

Agreed, there is a chance. But I guess in that case `8.jpg` will instead be named `08.jpg` ;). Anyway, I've added a link to the answer for more complex solutions. – Just Shadow Jun 16 '19 at 19:00

score 0 · Answer 2 · answered Jun 16 '19 at 18:49

A cleaner way of doing this would be to use System.IO.Path:

public IEnumerable<string> OrderFilesByNumberedName(IEnumerable<string> unsortedPathList) =>
    unsortedPathList
    .Select(path => new { name = Path.GetFileNameWithoutExtension(path), path }) // Get filename
    .OrderBy(file => int.Parse(file.name)) // Sort by number
    .Select(file => file.path); // Return only path

How to sort numbered filenames in list in C#

2 Answers2