Linq orderby, start with specific number, then return to lowest

Question

I have a set of data which I'd like to re-order starting with a specific number and then, when the highest number is reached, go back to the lowest and then carry on incrementing.

For example, for the sequence (1,2,3,4,5,6), if 4 was the specific number, the order would become (4,5,6,1,2,3).

Is that possible with linq & c#?

Answer 1

List<int> list = new List<int>() { 1, 2, 3, 4, 5, 6 };
int num = 4;
var newList = list.SkipWhile(x=>x!=num)
                    .Concat(list.TakeWhile(x=>x!=num))
                    .ToList();

Answer 2

int specific = 4;
var numbers = Enumerable.Range(1, 9);

var result = numbers.OrderBy(n => Tuple.Create(n < speficic, n)).ToList();

I use a little trick here, using Tuple<bool, int> as the comparer, since false < true. An alternative is:

var result = numbers.OrderBy(n => n < speficic).ThenBy(n => n).ToList();

EDIT after a benchmark I found the second solution .OrderBy .ThenBy is much faster than the Tuple solution. I believe it's because the FCL uses Comparer<T>.Default as the comparer, which costs time in constructing.