Hi Gary, On 2013-03-04, GaryMak <garymako...@googlemail.com> wrote: >> sage: Permutations(50).random_element() >> [11, 4, 30, 48, 49, 36, 22, 16, 27, 6, 44, 33, 13, 50, 9, 35, 15, 12, >> 26, 45, 1, 18, 2, 40, 19, 10, 28, 7, 37, 46, 25, 29, 34, 41, 38, 24, 8, >> 20, 32, 21, 14, 23, 31, 47, 43, 17, 3, 39, 5, 42] > > I have a set of size (say) 50 and I would like to generate a randomly-ordered > list of its elements. The trouble is, if I > use Permutations(my_set).random_element() it seems to want to generate the > whole lot of them before picking out a random > one!! Sorry but I cannot find how else to invoke this functionality, but I > know there must be a better way ....
Permutations(50).random_element() is quite fast, and I think it does *not* try to enumerate Sym(50). I'd do: sage: L = some list sage: p = Permutations(len(L)).random_element() sage: L_rand = [L[p[i]-1] for i in range(len(L))] Note that it is p[i]-1, because addressing list elements in Python is zero-based, but Permutations(50) permutes the numbers from 1 to 50, not from 0 to 49. Best regards, Simon -- You received this message because you are subscribed to the Google Groups "sage-support" group. To unsubscribe from this group and stop receiving emails from it, send an email to sage-support+unsubscr...@googlegroups.com. To post to this group, send email to sage-support@googlegroups.com. Visit this group at http://groups.google.com/group/sage-support?hl=en. For more options, visit https://groups.google.com/groups/opt_out.
