I'll contribute a little prose. Hopefully, it's helpful. In this particular case, notice that > transforms your list of boxes into a 5x6 table:
> (6?55);(6?55);(6?55);(6?55);(6?55) 13 4 19 43 3 52 10 1 4 46 52 11 38 12 48 50 54 45 36 54 39 35 53 50 44 1 7 54 11 41 So, we should be able to easily "reverse" the above, meaning that dealing with a 5x6 array is pretty much the same as dealing with 5 boxes of 6-arrays. Let's just keep this in mind for now, and first try to generate this 6x5 table. The key point of ? is that it's monadic and dyadic ranks are all 0, meaning that it transforms an array of integers into a corresponding array of random numbers: ? 50 6 $ 55 ... produces a random 50x6 array of integers each in the range i.55. This is not quite what we want, but we first note that it can be more idiomatically written: 50 6 ?@$ 55 The utility of @ (and @:) become a lot more apparent when writing tacit expressions. In general, x u@v y is equivalent to u (x v y), applying u "atop" x v y, hence the mnemonic. (NB. The difference between u@v and u@:v is that they produce verbs of different rank.) The dyad n?m produces n random numbers without replacement. Your posed problem is to generate 50 such lists, so conceptually we want to *reshape* the arguments of ? into 50-lists: (50$6) ? (50$55) but, better yet, as lots of verbs to ? will automatically reshape an atomic argument to the shape of the other argument, so we can abbreviate the above in one of two ways: 6 ? (50$55) NB. or (50$6) ? 55 In the first case, the parentheses are not necessary due to J parsing rules, so its more compact and idomatic to elide them 6 ? 50$55 These three previous options should produce the desired random tables. Now, putting things together, we just want to "redo" the boxing we did in the beginning example: <"1 (6 ? 50$55) Which should give the desired result. We need the parenthesis to separate the 1 from the 6, otherwise J would interpret this as <"1 6. Another way to break up the list lexing is like this: <"1 [ 6 ? 50 $ 55 Anyway, Hui's use of &. is even nicer. The key ideas is that u&.v first runs v on u's aguments and then *undoes* v on the result. The really neat thing is that > is a no-op on non-boxed atoms: > 42 42 So the idea is to let > be a no-op on our input array of integers, then let ? do it's thing, and finally *undo* > on *each* result. And since undoing > is simply doing <, we get what we want. 6 ?&.> 50 $ 55 The "each result" part above is exactly why this form is slick. ?&.> has the rank of >, i.e. 0 0 0. This means that it will box each list produced by ? as the integers are fed to it, which is exactly what we want in this case. Very cool stuff. Rank! Skip Cave <s...@caveconsulting.com> wrote: > Wow! Two completely different ways to generate multiple sets of random > integers. Roger used &. which I haven't really ever used or understood. I > will definitely need to understand &. for the future. Devon used @, which I > also haven't used very much. I need to find some practice and training > examples to work on both concepts. > > Skip Cave > Cave Consulting LLC > > > On Fri, Mar 13, 2020 at 12:04 AM Devon McCormick <devon...@gmail.com> wrote: > > > 6 5?@$55 > > Will give you a 6x5 table that is 6 independent rows of 5?55. > > > > > > On Fri, Mar 13, 2020 at 12:52 AM Roger Hui <rogerhui.can...@gmail.com> > > wrote: > > > > > 6 ?&.> 5 $ 55 > > > > > > > > ┌────────────────┬─────────────────┬───────────────┬─────────────────┬───────────────┐ > > > │47 28 45 25 8 36│22 40 23 20 11 49│15 16 42 38 4 5│50 45 38 37 13 28│42 > > 4 > > > 36 7 23 49│ > > > > > > > > └────────────────┴─────────────────┴───────────────┴─────────────────┴───────────────┘ > > > > > > 6 ?&.> 50 $ 55 > > > ... > > > > > > > > > On Thu, Mar 12, 2020 at 9:49 PM Skip Cave <s...@caveconsulting.com> > > wrote: > > > > > > > How can I generate the following result extended 50 times, without > > > explicit > > > > looping? > > > > > > > > (6?55);(6?55);(6?55);(6?55);(6?55) > > > > > > > > > > > > > > > > > ┌───────────────┬───────────────┬─────────────────┬─────────────────┬───────────────┐ > > > > > > > > │13 4 19 43 3 52│10 1 4 46 52 11│38 12 48 50 54 45│36 54 39 35 53 50│44 > > > 1 7 > > > > 54 11 41│ > > > > > > > > > > > > > > > > > └───────────────┴───────────────┴─────────────────┴─────────────────┴───────────────┘ > > > > > > > > > > > > > > > > Skip Cave > > > > Cave Consulting LLC > > > > ---------------------------------------------------------------------- > > > > For information about J forums see http://www.jsoftware.com/forums.htm > > > > > > > ---------------------------------------------------------------------- > > > For information about J forums see http://www.jsoftware.com/forums.htm > > > > > > > > > -- > > > > Devon McCormick, CFA > > > > Quantitative Consultant > > ---------------------------------------------------------------------- > > For information about J forums see http://www.jsoftware.com/forums.htm > > > ---------------------------------------------------------------------- > For information about J forums see http://www.jsoftware.com/forums.htm ---------------------------------------------------------------------- For information about J forums see http://www.jsoftware.com/forums.htm