Randomize a List problem

[John Keith]

(09-15-2020 06:39 PM)ijabbott Wrote:  Those two are the classic Fisher-Yates shuffle algorithm, with the ROLL and ROLLD exchanging two items at specified stack positions. Is there a more efficient way to swap stack elements?

In UserRPL I can't think of a faster way. Stack operations are generally faster than list operations.

There are two ListExt commands that are germane to the current discussion:

LSHUF implements the modern Fisher-Yates algorithm and is many times faster than any user implementation.

DOPERM lists all permutations of a list taken n items at a time (see documentation).

For instance, Albert's example of the 100th permutation of { 1 2 3 4 5 } would be

{ 1 2 3 4 5 } 5 << >> DOPERM 100 GET