How to sort filenames numerically in c#?

Question

I have several files in a folder. By default, they are displayed like this.

1.jpg
11.jpg
2.jpg
21.jpg
...

What I need is that the files are ordered numerically, taking as number to file name

1.jpg
2.jpg
11.jpg
21.jpg

My code

string path = Server.MapPath("./");
string[] files = Directory.GetFiles(path);

https://learn.microsoft.com/en-us/dotnet/api/system.linq.enumerable.orderby — Martheen, Jul 21 '22 at 21:30
You would need to extract the filename without extension, parse it to int (or maybe long if numbers exceed max int) and then order by that number. The other possibility is to add leading 0s to the names, so you force the alphabetical order to behave like a numerical one (as you do when naming files by date using YYYY-MM-DD format). — Fildor, Jul 21 '22 at 21:50
More specifically, `var files = Directory.GetFiles(path).OrderBy(n => Convert.ToInt32(Path.GetFileNameWithoutExtension(n)));` — NetMage, Jul 21 '22 at 22:15
Does this answer your question? [Natural Sort Order in C#](https://stackoverflow.com/questions/248603/natural-sort-order-in-c-sharp) — Charlieface, Jul 22 '22 at 00:38

score 1 · Accepted Answer · 2022-07-22T11:52:13.860

1

You could try:

string[] files = Directory.GetFiles(YourDirectory).OrderBy(f =>int.Parse(Path.GetFileNameWithoutExtension(f))).ToArray();

What this does is create an array, and for every file in a directory (YourDirectory in this example), it gets the file without the extension, and adds it to the list and orders it numerically. Check the source for more similar examples.

Source

edited Jul 22 '22 at 11:52

answered Jul 21 '22 at 22:30

Tank´s. this answer helped me to solve my problem – reynald27 Jul 29 '22 at 01:17

score 1 · Answer 2 · answered Jul 21 '22 at 23:40

you can use custom Comparer - sample:

using System.Text;

var directoryInfo = new DirectoryInfo(@"D:\test");
var fileInfoCollection = directoryInfo
    .GetFiles("*.txt")
    .OrderBy(x => x.Name, new AlphanumComparator());

PrintFiles(fileInfoCollection);

void PrintFiles(IEnumerable<FileInfo> files)
{
    foreach (var file in files)
    {
        Console.WriteLine(file.Name);
    }
}

and the core AlphanumComparator class for your problem - borrowed from stack (https://stackoverflow.com/a/5402865/1187755):

/*
 * The Alphanum Algorithm is an improved sorting algorithm for strings
 * containing numbers.  Instead of sorting numbers in ASCII order like
 * a standard sort, this algorithm sorts numbers in numeric order.
 *
 * The Alphanum Algorithm is discussed at http://www.DaveKoelle.com
 *
 * Based on the Java implementation of Dave Koelle's Alphanum algorithm.
 * Contributed by Jonathan Ruckwood <jonathan.ruckwood@gmail.com>
 *
 * Adapted by Dominik Hurnaus <dominik.hurnaus@gmail.com> to
 *   - correctly sort words where one word starts with another word
 *   - have slightly better performance
 *
 * Released under the MIT License - https://opensource.org/licenses/MIT
 *
 * Permission is hereby granted, free of charge, to any person obtaining
 * a copy of this software and associated documentation files (the "Software"),
 * to deal in the Software without restriction, including without limitation
 * the rights to use, copy, modify, merge, publish, distribute, sublicense,
 * and/or sell copies of the Software, and to permit persons to whom the
 * Software is furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included
 * in all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
 * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
 * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
 * IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM,
 * DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR
 * OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE
 * USE OR OTHER DEALINGS IN THE SOFTWARE.
 *
 */
public class AlphanumComparator : IComparer<string>
{
    private enum ChunkType { Alphanumeric, Numeric };
    private bool InChunk(char ch, char otherCh)
    {
        ChunkType type = ChunkType.Alphanumeric;

        if (char.IsDigit(otherCh))
        {
            type = ChunkType.Numeric;
        }

        if ((type == ChunkType.Alphanumeric && char.IsDigit(ch))
            || (type == ChunkType.Numeric && !char.IsDigit(ch)))
        {
            return false;
        }

        return true;
    }

    public int Compare(string x, string y)
    {
        string s1 = x;
        string s2 = y ;

        if (s1 == null || s2 == null)
        {
            return 0;
        }

        int thisMarker = 0, thisNumericChunk = 0;
        int thatMarker = 0, thatNumericChunk = 0;

        while ((thisMarker < s1.Length) || (thatMarker < s2.Length))
        {
            if (thisMarker >= s1.Length)
            {
                return -1;
            }
            else if (thatMarker >= s2.Length)
            {
                return 1;
            }
            char thisCh = s1[thisMarker];
            char thatCh = s2[thatMarker];

            var thisChunk = new StringBuilder();
            var thatChunk = new StringBuilder();

            while ((thisMarker < s1.Length) && (thisChunk.Length == 0 || InChunk(thisCh, thisChunk[0])))
            {
                thisChunk.Append(thisCh);
                thisMarker++;

                if (thisMarker < s1.Length)
                {
                    thisCh = s1[thisMarker];
                }
            }

            while ((thatMarker < s2.Length) && (thatChunk.Length == 0 || InChunk(thatCh, thatChunk[0])))
            {
                thatChunk.Append(thatCh);
                thatMarker++;

                if (thatMarker < s2.Length)
                {
                    thatCh = s2[thatMarker];
                }
            }

            int result = 0;
            // If both chunks contain numeric characters, sort them numerically
            if (char.IsDigit(thisChunk[0]) && char.IsDigit(thatChunk[0]))
            {
                thisNumericChunk = Convert.ToInt32(thisChunk.ToString());
                thatNumericChunk = Convert.ToInt32(thatChunk.ToString());

                if (thisNumericChunk < thatNumericChunk)
                {
                    result = -1;
                }

                if (thisNumericChunk > thatNumericChunk)
                {
                    result = 1;
                }
            }
            else
            {
                result = thisChunk.ToString().CompareTo(thatChunk.ToString());
            }

            if (result != 0)
            {
                return result;
            }
        }

        return 0;
    }
}

if you have time run benchmark :)

Result:

01.txt
1.txt
1a1.txt
1a2.txt
1a.txt
2.txt
3.txt
4.txt
11.txt
21.txt
aaa.txt
bbb01.txt
bbb02.txt
bbb.txt
test.txt
z.txt

How to sort filenames numerically in c#?

2 Answers2