--- George Russell <ger@tzi.de> wrote:

I think Ralf Hinze's method is the best presented so far. I would write it slightly differently though. In pseudo-code I would proceed as follows: (1) write the values to an array a[1]..a[n] (2) for i from n to 2 do j <- random integer between 1 and i swap a[i] and a[j] At the end the elements of a will be a random permutation. In Haskell you can of course use an STArray for this.

Ralf Hinze's method requires you to do n multiplications and n divisions to compute the factorial and then compute a random number. I have to compute n random numbers rather than a single random number, on the other hand I don't have to do the multiplications and divisions. Indeed, since you need more random bits to compute a random big number than a random little number, I don't think in theory my method requires much more work from the random number generator than Ralf Hinze's.

This is exactly how I did it in producing a randomised node-set in XSLT: "Randomization of node-sets or node-lists" http://www.topxml.com/code/default.asp?p=3&id=v20020504013704 ===== Cheers, Dimitre Novatchev. http://fxsl.sourceforge.net/ -- the home of FXSL __________________________________________________ Do you Yahoo!? Yahoo! Tax Center - forms, calculators, tips, more http://taxes.yahoo.com/