Is using Random and OrderBy a good shuffle algorithm?

Question

I have read an article about various shuffle algorithms over at Coding Horror. I have seen that somewhere people have done this to shuffle a list:

var r = ne         


        

Answer 1

I would say that many answers here like "This algorithm shuffles by generating a new random value for each value in a list, then ordering the list by those random values" might be very wrong!

I'd think that this DOES NOT assign a random value to each element of the source collection. Instead there might be a sort algorithm running like Quicksort which would call a compare-function approximately n log n times. Some sort algortihm really expect this compare-function to be stable and always return the same result!

Couldn't it be that the IEnumerableSorter calls a compare function for each algorithm step of e.g. quicksort and each time calls the function x => r.Next() for both parameters without caching these!

In that case you might really mess up the sort algorithm and make it much worse than the expectations the algorithm is build up on. Of course, it eventually will become stable and return something.

I might check it later by putting debugging output inside a new "Next" function so see what happens. In Reflector I could not immediately find out how it works.