A bit of terminology, here: Scan is the \ adverb (or, /\), Insert is /
We call / insert because it inserts its verb between the items of its right argument. For this example, that would be: 9 1 6 9 3 1 7 7 6 4 6 4 ([ -. -.) 3 1 5 8 8 5 4 7 7 5 2 5 ([ -. -.) 6 7 1 7 5 7 1 4 4 6 1 4 ([ -. -.) 9 1 5 2 0 7 6 6 2 9 5 1 ([ -. -.) 6 9 9 8 3 1 8 2 0 7 1 4 ([ -. -.) 9 7 9 1 1 8 1 2 1 5 1 6 Or, since mail is going to mutilate that long line, r0=: 9 1 6 9 3 1 7 7 6 4 6 4 r1=: 3 1 5 8 8 5 4 7 7 5 2 5 r2=: 6 7 1 7 5 7 1 4 4 6 1 4 r3=: 9 1 5 2 0 7 6 6 2 9 5 1 r4=: 6 9 9 8 3 1 8 2 0 7 1 4 r5=: 9 7 9 1 1 8 1 2 1 5 1 6 r0 ([ -. -.) r1 ([ -. -.) r2 ([ -. -.) r3 ([ -. -.) r4 ([ -. -.) r5 1 1 7 7 Anyways, now that things are split out like that, we can look at intermediate results: r4 ([ -. -.) r5 6 9 9 8 1 8 2 7 1 r3 ([ -. -.) r4 ([ -. -.) r5 9 1 2 7 6 6 2 9 1 r2 ([ -. -.) r3 ([ -. -.) r4 ([ -. -.) r5 6 7 1 7 7 1 6 1 r1 ([ -. -.) r2 ([ -. -.) r3 ([ -. -.) r4 ([ -. -.) r5 1 7 7 (We could have also gotten intermediate results using ([ -. -.)/\. but if we did it that way they would have been padded with zeros.) I hope this helps, -- Raul On Sat, Sep 2, 2017 at 5:19 PM, Skip Cave <s...@caveconsulting.com> wrote: > Raul. > > Wow! I never realized what the dyadic use of "-." (less) would do. That is > really neat. Plus I keep forgetting that insert will work with all kinds of > verbs, not just + * >. and the other usual primitive suspects. > > However I'm still trying to wrap my head around this: ([-.-.)/a > So I tried some experiments: > > ]a =: ?6 12$10 > > 9 1 6 9 3 1 7 7 6 4 6 4 > > 3 1 5 8 8 5 4 7 7 5 2 5 > > 6 7 1 7 5 7 1 4 4 6 1 4 > > 9 1 5 2 0 7 6 6 2 9 5 1 > > 6 9 9 8 3 1 8 2 0 7 1 4 > > 9 7 9 1 1 8 1 2 1 5 1 6 > > > >./([-.-.)/a > > 7 > > <./([-.-.)/a > > 1 > > > > NB. Yes, the whole thing works as advertised. > > NB. So let's deconstruct it: > > > > ([-.-.)/a > > 1 1 7 7 > > > NB. So this clearly finds all the common integers across all the rows. > > NB. But why are there two ones and two sevens? There is only > > NB. one one in the second row, and three sevens in the third row. > > NB, And only one seven in the fourth, fifth, sixth, and seventh row. > > > NB. So let's see what happens if we remove the parenthesis: > > > [-.-./a > > _8 _5 _8 _5 _3 _5 _3 > > > NB. Whoa! Seven numbers?? There are 6 rows and 12 columns. What happened? > > NB. Let's try this... > > > -.-./a > > _8 _5 _8 _5 _3 _5 _3 > > > NB. So the square bracket doesn't make any difference. > > > -. 9 1 6 9 3 1 7 7 6 4 6 4 NB. try on the first row of matrix a > > _8 0 _5 _8 _2 0 _6 _6 _5 _3 _5 _3 > > > NB. That looks a little bit like the previous result with no parenthesis. > > NB. Well, that's just what the Vocabulary says will happen (-.y is 1-y): > > 1 - 9 1 6 9 3 1 7 7 6 4 6 4 > > _8 0 _5 _8 _2 0 _6 _6 _5 _3 _5 _3 > > > NB. So now we put the scan back in: > > -./ 9 1 6 9 3 1 7 7 6 4 6 4 > > 9 > > > NB. That makes sense, since: > > 9-.1-.6-.9-.3-.1-.7-.7-.6-.4-.6-.4 > > 9 > > > NB. Let's try two -.s > > -.-./ 9 1 6 9 3 1 7 7 6 4 6 4 > > _8 > > > NB. That makes sense, since -. 9 -> _8 > > > But I still can't figure out what scan is doing to the noun a. > > > Skip > > > > > > > > > > > > > > > > (-.-.)/a > > 9 1 6 9 3 1 7 7 6 4 6 4 > > > > > Skip Cave > Cave Consulting LLC > > On Fri, Sep 1, 2017 at 2:21 AM, Raul Miller <rauldmil...@gmail.com> wrote: > >> If it exists, >./([-.-.)/a will find the largest integer common to all >> of the rows. (If it does not exist, it will give you __ which is the >> identity element for "largest". In other words, __ >. x always returns >> x). >> >> To get the smallest replace >. with <. >> >> In other words, first find the intersection of all rows, then find the >> largest (or smallest) number in that intersection. >> >> Thanks, >> >> -- >> Raul >> >> >> On Fri, Sep 1, 2017 at 2:48 AM, Skip Cave <s...@caveconsulting.com> wrote: >> > This wasn't a Quora problem, though I needed to solve this as part of the >> > solution to a different problem. >> > >> > Given the random integer matrix: >> > >> > ]a =: 6 12$ ?72$10 >> > >> > 2 3 6 6 5 8 3 7 4 9 0 8 >> > >> > 1 9 4 1 7 3 1 8 2 5 2 7 >> > >> > 4 7 4 7 6 4 1 1 4 6 6 8 >> > >> > 5 8 0 0 3 1 8 3 0 7 3 3 >> > >> > 4 4 7 3 2 4 7 5 7 3 3 9 >> > >> > 3 8 4 1 3 7 8 7 5 6 9 9 >> > >> > >> > What J expression will find the largest integer that is common to all >> > >> > of the rows? In this specific case, the answer is 7. >> > >> > What about the smallest integer that's common in all rows? >> > >> > >> > Skip >> > ---------------------------------------------------------------------- >> > 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 ---------------------------------------------------------------------- For information about J forums see http://www.jsoftware.com/forums.htm
