C# string operation. get file name substring

Question

myfinename_slice_1.tif
myfilename_slice_2.tif
...
...
myfilename_slice_15.tif
...
...
myfilename_slice_210.tif

In C#, how can I get file index, like "1", "2", "15", "210" using string operations?

Describe your parameters. Does the number always occur at the end of the filename, just before the file extension, after an underscore character? — Michael Petrotta
– Michael Petrotta, Commented Nov 4, 2011 at 17:38
@micheal, yes, number always appear before extention, and after slice_, but maybe 1 digit or 2 or 3 digtis. — Anders Lind
– Anders Lind, Commented Nov 4, 2011 at 17:41

João Angelo · Accepted Answer · 2011-11-04 17:45:41Z

5

You have some options:

Regular expressions with the Regex class;
String.Split.

Most important is what are the assumptions you can make about the format of the file name.

For example if it's always at the end of the file name, without counting the extension, and after an underscore you can do:

var id = Path.GetFileNameWithoutExtension("myfinename_slice_1.tif")
    .Split('_')
    .Last();

Console.WriteLine(id);

If for example you can assume that the identifier is guaranteed to appear in the filename and the characters [0-9] are only allowed to appear in the filename as part of the identifier, you can just do:

var id = Regex.Match("myfinename_slice_1.tif", @"\d+").Value;

Console.WriteLine(id);

There are probably more ways to do this, but the most important thing is to assert which assumptions you can make and then code a implementation based on them.

edited Nov 4, 2011 at 17:45

answered Nov 4, 2011 at 17:39

João Angelo

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Comments

Jacob · Accepted Answer · 2011-11-04 17:42:08Z

2

This looks like a job for regular expressions. First define the pattern as a regular expression:

.*?_(?<index>\d+)\.tif

Then get a match against your string. The group named index will contain the digits:

var idx = Regex.Match(filename, @".*?_(?<index>\d+)\.tif").Groups["index"].Value;

answered Nov 4, 2011 at 17:42

Jacob

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eldarerathis · Accepted Answer · 2011-11-04 17:40:43Z

1

You can use the regex "(?<digits>\d+)\.[^\.]+$", and if it's a match the string you're looking for is in the group named "digits"

edited Nov 4, 2011 at 17:40

eldarerathis

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answered Nov 4, 2011 at 17:39

Iesvs

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Artak · Accepted Answer · 2011-11-04 17:46:47Z

1

Here is the method which will handle that:

public int GetFileIndex(string argFilename) { return Int32.Parse(argFilename.Substring(argFilename.LastIndexOf("_")+1, argFilename.LastIndexOf("."))); }

Enjoy

answered Nov 4, 2011 at 17:46

Artak

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fardjad · Accepted Answer · 2011-11-04 17:39:33Z

0

String.Split('_')[2].Split('.')[0]

answered Nov 4, 2011 at 17:39

fardjad

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Aaron Anodide · Accepted Answer · 2011-11-04 19:30:57Z

public class UnitTest1
{
    [TestMethod]
    public void TestMethod1()
    {
        var s1 = "myfinename_slice_1.tif";
        var s2 = "myfilename_slice_2.tif";
        var s3 = "myfilename_slice_15.tif";
        var s4 = "myfilename_slice_210.tif";
        var s5 = "myfilena44me_slice_210.tif";
        var s6 = "7myfilena44me_slice_210.tif";
        var s7 = "tif999";
        Assert.AreEqual(1, EnumerateNumbers(s1).First());
        Assert.AreEqual(2, EnumerateNumbers(s2).First());
        Assert.AreEqual(15, EnumerateNumbers(s3).First());
        Assert.AreEqual(210, EnumerateNumbers(s4).First());
        Assert.AreEqual(210, EnumerateNumbers(s5).Skip(1).First());
        Assert.AreEqual(210, EnumerateNumbers(s6).Skip(2).First());
        Assert.AreEqual(44, EnumerateNumbers(s6).Skip(1).First());
        Assert.AreEqual(999, EnumerateNumbers(s7).First());
    }

    static IEnumerable<int> EnumerateNumbers(string input)
    {
        var digits = new char[] { '0', '1', '2', '3', '4', '5', '6', '7', '8', '9' };
        string result = string.Empty;
        foreach (var c in input.ToCharArray())
        {
            if (!digits.Contains(c))
            {
                if (!string.IsNullOrEmpty(result))
                {
                    yield return int.Parse(result);
                    result = string.Empty;
                }
            }
            else
            {
                result += c;      
            }
        }
        if (result.Length > 0) 
            yield return int.Parse(result);
    }
}

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