Shorter way to order a list by boolean functions

Question

I have a list that needs to be ordered in a specific way. I've currently solved it like this:

var files = GetFiles()
  .OrderByDescending(x => x.Filename.StartsWith("ProjectDescription_"))
  .ThenByDescending(x => x.Filename.StartsWith("Budget_"))
  .ThenByDescending(x => x.Filename.StartsWith("CV_"))
  .ToArray();

The files are going to be merged into a single PDF file and the point here is that certain files should come at the beginning, and the rest at the end.

I'm wondering if there is a better way to write this "pattern", cause it feels rather blah and would become even more blah if there were more cases.

---

Things I'd like to avoid, but not sure how: Multiple passes through the list, more StartsWith calls per file than necessary, more code than necessary, etc.

Basically I think I'd like an OrderByPredicates sort of thing which smartly fulfilled those criteria and whose API was used sort of like this:

var predicates = new Func<boolean, File>[] {
  x => x.Filename == "First"
  x => x.Filename.StartsWith("Foo_"),
  x => x.Filename.StartsWith("Bar_"),
};

var files = GetFiles()
  .OrderByPredicates(predicates)
  .ThenBy(x => x.Filename);

Answer 1

Compact (except for a little helper method) and easy to extend:

private static readonly string[] Prefixes = {"ProjectDescription_", "Budget_", "CV_"};

public static int PrefixIndex(string name)
{
  for (int i = 0; i < Prefixes.Length; i++)
  {
    if (name.StartsWith(Prefixes[i]))
    {
      return i;
    }
  }
  return int.MaxValue;
}

// ...

var files = GetFiles().OrderBy(x => PrefixIndex(x.Name));