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 B A C B C D E 

And these variables:

string firstPref, secondPref, thirdPref;

When the values are set like so:

firstPref = 'A'; secondPref = 'B'; thirdPref = 'C'; 

Is it possible to order the data like so:

A A B B C C D E 

Answer 1

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

List<String> data = new List<String> { "A","B","A","C","B","C","D","E" }; List<String> preferences = new List<String> { "A","B","C" };  IEnumerable<String> 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<String> orderedData = data.OrderByDescending(    item => Enumerable.Reverse(preferences).ToList().IndexOf(item)); 

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

IEnumerable<String> 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.

Answer 2

In addition to @Daniel Brückner answer and problem defined at the end of it:

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.

I think that the solution is to use a statement lambda instead of an expression lambda.

var data = new List<string> { "corge", "baz", "foo", "bar", "qux", "quux" }; var fixedOrder = new List<string> { "foo", "bar", "baz" }; data.OrderBy(d => {                     var index = fixedOrder.IndexOf(d);                     return index == -1 ? int.MaxValue : index;                    }); 

The ordered data is:

foo  bar  baz  corge  qux  quux