Custom Linq Ordering

Question

I have over a thousand folders, each folder contains one or more files with the following names:

Unordered:

Alison.ext
Heather.ext
Molly.ext
Paula.ext
Sam.ext

Ordered:

Molly.ext
Sam.ext
Heather.ext
Alison.ext
Paula.ext

I would like to write an expression to sort this list as described above.

Answer 1

//Creating a dictionary with the custom order
var order = "MSHAP";
var orderDict = order.Select((c,i)=>new {Letter=c, Order=i})
                     .ToDictionary(o => o.Letter, o => o.Order);

var list = new List<string>{"A.ext", "H.ext", "M.ext", "P.ext", "S.ext"};

//Ordering by the custom criteria
var result = list.OrderBy(item => orderDict[item[0]]);

Instead of calling orderDict[item[0]] you could have a nice helper method that cares for the fringe cases (non existent letters, null, and so on). But that's the idea.

Answer 2

Here's a method that produces keys for ordering

public int OrderKey(string fileName)
{
  char first = fileName[0];
  int result =
     first  == 'M' ? 1 :
     first  == 'S' ? 2 :
     first  == 'H' ? 3 :
     first  == 'A' ? 4 :
     first  == 'P' ? 5 :
     6;
  return result;
}

Here's how to call it:

List<File> ordered = Files.OrderBy(f => OrderKey(f.FileName)).ToList();

Answer 3

List<char> sortKeys = new List<char> { 'M', 'S', 'H', 'A', 'P' };
sortKeys.Reverse();
List<FileInfo> files = new List<FileInfo>(6);

foreach(char sortKey in sortKeys)
{
    var topFiles = files.Where(file => file.Name.StartsWith(sortKey.ToString()));
    var remainingFiles = files.Except(topFiles);
    files = topFiles.Concat(remainingFiles).ToList();
}

Untested and I'm sure there are faster ways, but at least it's with linq stuff as you asked :-)

edit: I just saw the edit on your post and now I don't have any idea anymore what you really want to do, so my code is probably useless to you..