Why does using Random in Sort causing [Unable to sort IComparer.Compare error]

Question

I tried shuffling a list of byte (List) using either code:

myList.Sort((a, b) => this._Rnd.Next(-1, 1));

or

myList.Sort         


        

Answer 1

Not only is the comparison relation required to be consistent, it is also required to impose a total ordering. For example, you cannot say "socks are smaller than shoes, shirts are neither smaller than nor greater than trousers" blah blah blah, feed that into a sort algorithm and expect to get a topological sort out of the other end. Comparison sorts are called comparison sorts because they require a well-formed comparison relation. In particular, quicksort can run forever or give nonsensical results if the comparison relation is not consistent, transitive, and total-ordering.

If what you want is a shuffle then implement a Fischer-Yates shuffle. (Do it correctly; even though the algorithm is trivial, it is almost always implemented wrong.) If what you want is a topological sort then implement a topological sort. Use the right tool for the job.