How to use LINQ to return substring of FileInfo.Name

Question

I would like to convert the below "foreach" statement to a LINQ query that returns a substring of the file name into a list:

IList<string> fileNameSubstringValues = new List<string>();

//Find all assemblies with mapping files.
ICollection<FileInfo> files = codeToGetFileListGoesHere;

//Parse the file name to get the assembly name.
foreach (FileInfo file in files)
{
    string fileName = file.Name.Substring(0, file.Name.Length - (file.Name.Length - file.Name.IndexOf(".config.xml")));
    fileNameSubstringValues.Add(fileName);
}

The end result would be something similar to the following:

IList<string> fileNameSubstringValues = files.LINQ-QUERY-HERE;

There's no query here, just a transformation from A[] to B[]. — Jay Bazuzi
– Jay Bazuzi, Commented Jan 6, 2009 at 21:24

Christian C. Salvadó · Accepted Answer · 2009-01-06 21:19:58Z

6

Try something like this:

var fileList = files.Select(file =>
                            file.Name.Substring(0, file.Name.Length -
                            (file.Name.Length - file.Name.IndexOf(".config.xml"))))
                     .ToList();

answered Jan 6, 2009 at 21:19

Christian C. Salvadó

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3 Comments

Jay Bazuzi Over a year ago

Voted up: I prefer the extension method syntax to the query syntax here, since there's really no query: your goal is to perform a transform on all the elements. There's no 'where' or 'orderby' or a crossing 'select' even 'select new { x, y }.

Christian C. Salvadó Over a year ago

@Jay, I also prefer the extension method syntax for simple projections, the query syntax I think I only use it when doing joins...

user1228 Over a year ago

better because 1) fluent interface 2) no brackets around the query needed

casperOne · Accepted Answer · 2009-01-06 21:17:32Z

2

IList<string> fileNameSubstringValues =
  (
    from 
      file in codeToGetFileListGoesHere
    select 
      file.Name.
        Substring(0, file.Name.Length - 
          (file.Name.Length - file.Name.IndexOf(".config.xml"))).ToList();

Enjoy =)

answered Jan 6, 2009 at 21:17

casperOne

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Comments

Jay Bazuzi · Accepted Answer · 2009-01-06 23:34:01Z

If you happen to know the type of the collection of FileInfos, and it's a List<FileInfo>, I'd probably skip the Linq and write:

        files.ConvertAll(
            file => file.Name.Substring(0, file.Name.Length - (file.Name.Length - file.Name.IndexOf(".config.xml")))
            );

or if it's an array:

        Array.ConvertAll(
            files,
            file => file.Name.Substring(0, file.Name.Length - (file.Name.Length - file.Name.IndexOf(".config.xml")))
            );

Mainly because I like saying "Convert" instead of "Select" to express my intent to a programmer reading this code.

However, Linq is part of C# now, so I think it's perfectly reasonable to insist that a reading programmer understand what Select does. And the Linq approach lets you easily migrate to PLinq in the future.

Robert C. Barth · Accepted Answer · 2009-01-07 00:06:42Z

1

FYI,

file.Name.Substring(0, file.Name.Length - (file.Name.Length - file.Name.IndexOf(".config.xml")))

is the same as

file.Name.Substring(0, file.Name.IndexOf(".config.xml"));

Also, if that string ".config.xml" appears before the end of the file name, your code will probably return the wrong thing; You should probably change IndexOf to LastIndexOf and check that the index position returned + 11 (the size of the string) == length of the filename (assuming you're looking for files ending in .config.xml and not just files with .config.xml appearing somewhere in the name).

answered Jan 7, 2009 at 0:06

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