Linq OrderBy against specific values

Question

Is there a way in Linq to do an OrderBy against a set of values (strings in this case) without knowing the order of the values?

Consider this data:

A         


        

Answer 1

If you put your preferences into a list, it might become easier.

List data = new List { "A","B","A","C","B","C","D","E" };
List preferences = new List { "A","B","C" };

IEnumerable orderedData = data.OrderBy(
   item => preferences.IndexOf(item));

This will put all items not appearing in preferences in front because IndexOf() returns -1. An ad hoc work around might be reversing preferences and order the result descending. This becomes quite ugly, but works.

IEnumerable orderedData = data.OrderByDescending(
   item => Enumerable.Reverse(preferences).ToList().IndexOf(item));

The solution becomes a bit nicer if you concat preferences and data.

IEnumerable orderedData = data.OrderBy(
   item => preferences.Concat(data).ToList().IndexOf(item));

I don't like Concat() and ToList() in there. But for the moment I have no really good way around that. I am looking for a nice trick to turn the -1 of the first example into a big number.