如何在linq查询中排序？

Question

So I am getting some files like this:

int pathLength = path.Length + 1;
var files = Directory.GetFiles ( path, "*.*", SearchOption.AllDirectories )
    .Where ( s => s.EndsWith ( ".bmp", StringComparison.OrdinalIgnoreCase ) ||
        s.EndsWith ( ".jpg", StringComparison.OrdinalIgnoreCase ) )
        .Select ( s => s.Substring ( pathLength, s.Length - pathLength ) )

    .ToList ( );

and was before sorting like this:

FileComparer fileComparer = new FileComparer ( );
files.Sort ( fileComparer );

But for Sort I need to use ToList. I am wondering if I can just add the Sort to the Linq the same way and get rid of ToList?

Answer 1

You're looking for the OrderBy method :

var extensions = new HashSet<string>(StringComparer.OrdinalIgnoreCase) { ".bmp", ".jpg" };
int pathLength = path.Length + 1;
var files = Directory.EnumerateFiles(path, "*.*", SearchOption.AllDirectories)
    .Where(s => extensions.Contains(Path.GetExtension(s)))
    .Select(s => s.Substring(pathLength))
    .OrderBy(s => s, new FileComparer());

You can replace your FileComparer class with

.OrderBy(s => !s.Contains('\\')).ThenBy(s => s)

Since false < true , this will sort strings that start with \\\\ before other ones.

Answer 2

Use OrderBy method.

Your code will change from -

files.Sort((x, y) => string.Compare(x.fileName, y.fileName));

to -

files.OrderBy(x => x.fileName);

Update

files.OrderBy(x => x.fileName.Contains(@"\\")).ThenBy(x => x.fileName);

Answer 3

.OrderBy(f => f, new FileComparer())

（这假设FileComparer实现了IComparer<string> ）

Answer 4

There's a few things you can do to improve your code :

• like said previously, use OrderBy for sort

• write your request as a LINQ expression rather than successive method calls :

   var files = (from file in Directory.GetFiles ( path, "*.*", SearchOption.AllDirectories ) where file.EndsWith ( ".bmp", StringComparison.OrdinalIgnoreCase ) || file.EndsWith ( ".jpg", StringComparison.OrdinalIgnoreCase ) orderby new FileComparer() select file); 

  The code above does the same than yours but is more elegant.

• To get path, extension, file name... I strongly recommend you to use System.IO.Path helpers methods rather than perform string operations like substring or contains !!

• Rather than use Directory.GetFiles you could instantiate a DirectoryInfo and call the GetFiles method : this one has the advantage to return an array of FileInfo, which exposes directly properties like extension, file name...

Hope this helps