By the way, if you want to add up the array of (+!)s of digits, you should use +/"1 instead of +/@:|: . It's much faster and prettier.
Marshall -----Original Message----- From: [email protected] [mailto:[email protected]] On Behalf Of Alex Gian Sent: Sunday, August 29, 2010 12:05 PM To: Programming forum Subject: Re: [Jprogramming] Splitting an integer into its digits Hi Ric and all, There's one more thing I'd like to mention, now that I got this 'rank' thing sorted: I don't know if you noticed, but adding "0 to the 'digits' verb, has some interesting, and IMHO not very acceptable effects on time and space taken. For instance, finding specials <10e5 is instantaneous on my desktop machine without the "0, yet takes about 7 seconds when done the other way. in the process it uses all of my 2Gb memory! (OK, without the "0 means using the ugly transpose method AND getting the wrong results for leading zeros, but still. I guess J really does prefer big arrays!!) Trying to find all specials <10e6, eats up all mem PLUS my 6Gb swap space without achieving a result. Without the "0 I get the result 1n 2 seconds, albeit with the wrong value for numbers with leading-zeros. On my PDA (Acer n30, which is my main J learning platform), it doesn't even finish without the "0, complains it's out of memory. I dragged out my old Jornada 928 (J502) and it managed to finish here, probably a bit more memory available. Took 18 seconds on what is basically a 206MHz ARM. In comparison, my Nokia 770, with a 260MHZ ARM, solves the same problem iteratively, in Perl, in 28 seconds, without taking any space at all. I don't think this reflects too well on J. I suppose what I'm asking is: is there another (neat J-like) way to do searches, other than using # over huge arrays, that would take up little (preferably constant) space for this class of problems? On Sun, 2010-08-29 at 02:35 +1200, Sherlock, Ric wrote: > If you add the "0 to digits, you don't need to use the transpose because +/ is only ever getting fed a list (rank 1). > > digits=: 10&#.^:_1"0 > fp1=: + ! > spsum=: +/@f...@digits > special=: = spsum > (#~ special) 1974 123 85837 408297 > 85837 408297 > > special f. > = +/@(+ !)@(10&#.^:_1"0) > > IOW a one-liner for special would be: > special2=: = +/@(+ !)@(10&#.^:_1"0) > (#~ special2) 1974 123 85837 408297 > 85837 408297 > > ---------------------------------------------------------------------- > 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
