randomize a list
in [Lisp]
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From: x on 2 Aug 2010 14:24 Haris Bogdanovi� <fbogdanovic(a)xnet.hr> wrote in news:i343g1$gc1$1 @gregory.bnet.hr: > How to randomize a list ? One way would be to shuffle it like playing cards. Divide the list in two then pop from each at random to make a new list. Most lisps work with lists much faster than other data structures because they recycle cons cells. How many times you have to shuffle is proportional to the log of the length of the list. A deck of playing cards should be shuffled more than five times because each shuffle is not perfectly random because clumsy fingers let several cards move together. But less than five times because card players don't care if it's perfectly random. It would be interesting to time it vs other methods, for different lengths of lists.
From: josephoswald+gg on 2 Aug 2010 15:01
On Aug 1, 9:18 pm, w_a_x_man <w_a_x_...(a)yahoo.com> wrote: > On Aug 1, 10:22 am, Haris Bogdanoviæ <fbogdano...(a)xnet.hr> wrote: > > > Hi. > > > How to randomize a list ? > > > Thanks > > (1..9).sort_by{ rand } > [7, 1, 3, 5, 9, 2, 6, 8, 4] Even in Ruby this approach is buggy. It does not select each permutation with equal likelihood. But hey, if you can't pay attention to the name of the newsgroup, why would you pay attention to other matters of correctness? http://eigenclass.org/hiki/sort_by+rand+is+biased |