I was writing some code today to map online drive and files to a local objecttree. So I created a custom file and directory object and a directory holds subdirectories and files.

Something like this:

public class File
{
    public string Name { get; set; }
}

public class Directory
{
    public string Name { get; set; }
    public List<Directory> SubDirectories { get; set; }
    public List<File> Files { get; set; }
}

Now I wanted to have a method which tells me how many files are in a folder, including all the subfolders. This is essentially a recursive select of the number of files per directory and then the sum of the files.

So I implemented a LINQ statement:

public int GetNumberOfFiles()
{
    int total = ( from dir in SubDirectories
                  select dir.Files.Count ).Sum();
    return total;
}

Now this will only get the sum of the number of files in the directories immediately below the current. Let's add a little recursion:

public int GetNumberOfFiles()
{
    int total = ( from dir in SubDirectories
                  select dir.Files.Count + dir.GetNumberOfFiles() ).Sum();
    return total;
}

Pretty nifty!