Question

Can someone tell me what I’m doing wrong with the following Linq query? I’m trying to find the directory with the highest aphanumerical value.

        DirectoryInfo[] diList = currentDirectory.GetDirectories();

        var dirs = from eachDir in diList
                   orderby eachDir.FullName descending                    
                   select eachDir;
        MessageBox.Show(dirs[0].FullName);

EDIT:

The above code does not compile, the error that the compiler generates is:

Cannot apply indexing with [] to an expression of type 'System.Linq.IOrderedEnumerable<System.IO.DirectoryInfo>

Answer 1

You’re trying to access dirs as if it were an array or a list. It’s just an IEnumerable<T>. Try this:

var dirs = diList.OrderByDescending(eachDir => eachDir.FullName);
var first = dirs.FirstOrDefault();
// Now first will be null if there are no directories, or the first one otherwise

Note that I haven’t used a query expression here because it seems pretty pointless for just a single clause. You could put it all into one statement, too:

var first = currentDirectory.GetDirectories()
                            .OrderByDescending(eachDir => eachDir.FullName)
                            .FirstOrDefault();