NULL or the number of tied values (including NA). Providing nties can speed-up when x has no cache. Note that a wrong nties can cause undefined behaviour up to a crash.
NULL for automatic method selection or a suitable low-level method, see details
an integer vector of positions
This function automatically chooses from several low-level functions considering the size of x and the availability of a cache.
Suitable methods are sortordertie (fast ordering)
and ordertie (memory saving ordering).