C# Sorting a FileInfo Array by Name, getting some unexpected results and need to know if I have other sorting options available

Question

I am saving my image files in the following format: 1-6784 (1 being the sort order that I want to see and 6784 being a randomly generated number between 1000 and 9999.

When I look at the folder through explorer and arrange by name they all look fine and sorted according to the first number i.e. (1-XXXX, 2-XXXX , 9-XXXX, 12-XXXX etc.) in ascending order.

However when I get the FileInfo array for this directory it automatically sorts it by name I presume, but it for some reason would place 10-XXXX and 11-XXXX before 1-XXXX, 2-XXXX etc. So up until 10 it's fine and the order retains when image src links are generated in the view in my web application, but once I upload\save more than 9 files the double digit 10, 11 etc. take front spots in the array over the single digit numbers.

DirectoryInfo sourceDir = new DirectoryInfo(System.Web.HttpContext.Current.Request.MapPath("~/Content/ProductImages/" + Model.Products[i].ProductID.ToString() + "/thumbs/"));

                   if (sourceDir.Exists)
                   {

                       FileInfo[] fileEntries = sourceDir.GetFiles();
                       Array.Sort(fileEntries, (f1, f2) => f1.Name.CompareTo(f2.Name));


}

Community · Accepted Answer · 2017-04-12 07:31:17Z

4

Description

You sort a string and this is the right result.

That is lexicographic sorting which means basically the language treats the variables as strings and compares character by character ("200" is greater than "19999" because '2' is greater than '1') ...

Source Why do some sorting methods sort by 1, 10, 2, 3…?

Solution

I suggest you create a custom Comparer which pads leading zeros to the fileName.

public class MyCustomComparer : IComparer<FileInfo>
{
    public int Compare(FileInfo x, FileInfo y)
    {
        // split filename
        string[] parts1 = x.Name.Split('-');
        string[] parts2 = y.Name.Split('-');

        // calculate how much leading zeros we need
        int toPad1 = 10 - parts1[0].Length;
        int toPad2 = 10 - parts2[0].Length;

        // add the zeros, only for sorting
        parts1[0] = parts1[0].Insert(0, new String('0', toPad1));
        parts2[0] = parts2[0].Insert(0, new String('0', toPad2));

        // create the comparable string
        string toCompare1 = string.Join("", parts1);
        string toCompare2 = string.Join("", parts2);

        // compare
        return toCompare1.CompareTo(toCompare2);
    }
}

And call them

FileInfo[] fileEntries = sourceDir.GetFiles();
Array.Sort(fileEntries, new MyCustomComparer());

More Information

MSDN - IComparer Interface

edited Apr 12, 2017 at 7:31

CommunityBot

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answered Feb 16, 2012 at 12:55

dknaack

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1 Comment

LaserBeak Over a year ago

So I would somehow need to convert the sortorder to int and sort by that. Any quick and graceful way of doing that in my case?

the_joric · Accepted Answer · 2012-02-16 13:02:28Z

3

You need to pad your sort order with leading zeros:

0001-XXX
0002-XXX
...

Or you may try the following to sort your exiting files:

FileInfo[] fileEntries = sourceDir.GetFiles()
   .OrderBy(f => Regex.Match(f.Name, "^[0-9]+").Value.PadLeft(10, '0'))
   .ToArray();

edited Feb 16, 2012 at 13:02

answered Feb 16, 2012 at 12:56

the_joric

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Comments

Alexey Raga · Accepted Answer · 2012-02-16 12:57:53Z

1

The reason is clear: the file name is a string, and as a string "11" comes after "1" but before "2".

In order to do what you want, in your comparison function you will need to parse the name and compare parts (separated by dash) as numbers (simply cast and compare)

answered Feb 16, 2012 at 12:57

Alexey Raga

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Comments

dana · Accepted Answer · 2012-02-16 18:23:44Z

1

You could parse out the numbers and compare them as follows:

DirectoryInfo sourceDir = new DirectoryInfo(System.Web.HttpContext.Current.Request.MapPath("~/Content/ProductImages/" + Model.Products[i].ProductID.ToString() + "/thumbs/"));

if (sourceDir.Exists)
{
    FileInfo[] fileEntries = sourceDir.GetFiles();
    Array.Sort(fileEntries,
        delegate(FileInfo x, FileInfo y)
        {
            String[] xvals = x.Name.Split('-');
            String[] yvals = y.Name.Split('-');

            int cmp = Int32.Parse(xvals[0]).CompareTo(Int32.Parse(yvals[0]));
            if (cmp != 0)
            {
                return cmp;
            }

            cmp = Int32.Parse(xvals[1]).CompareTo(Int32.Parse(yvals[1]));
            return cmp;
        }
    );
}

edited Feb 16, 2012 at 18:23

answered Feb 16, 2012 at 12:59

dana

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Comments

spender · Accepted Answer · 2012-02-16 12:57:32Z

0

How about pre-padding your numbers with zeroes, so that they are fixed length. This way alphanumeric comparison will yield the same result as the numeric comparison you are expecting.

answered Feb 16, 2012 at 12:57

spender

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Comments

Sir Crispalot · Accepted Answer · 2012-02-16 12:59:48Z

0

If you don't want to change your file names, you could do the padding during the comparison. I chose to pad it to ten numbers, but it may need to be more depending on how many files you have.

Array.Sort(fileEntries, (f1, f2) => f1.Name.PadLeft(10, '0').CompareTo(f2.Name.PadLeft(10, '0'));

answered Feb 16, 2012 at 12:59

Sir Crispalot

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