I've used "catalog" in real-world apps but, as Dan indicates, it was with arguments that gave fairly small results.
On Thu, May 8, 2014 at 8:30 PM, 'Pascal Jasmin' via Programming < [email protected]> wrote: > > one reason for its rarity is, at least, that in any real-world context, > a complete MxN catalog would be prohibitively expensive > > its very cheap compared to A. and filtering permutations after you've > generated them. In the resource matching application I linked to, where 1 > user ends up with 1 resource, its also possible to prefilter the arguments > to catalogue removing options where forced choices exist, and thus > significantly reducing an exponential algorithm to allow solutions to > moderately large problem spaces. > > Its fast compared to backtracking loop solutions in other languages even > when they abort after finding first valid set of matches. It seems like a > very clean J way of approaching fairly hard problems. Polynomial and > higher problems benefit from strategies that reduce search space. > > Using catalogue to analyze n moves with an average x possibilities per > move has an expensive x ^ n search space. But reducing any move > possibility to 1 reduces both average x, and reduces n by 1 > > > ----- Original Message ----- > From: Dan Bron <[email protected]> > To: "[email protected]" <[email protected]> > Cc: > Sent: Thursday, May 8, 2014 6:39:14 PM > Subject: Re: [Jprogramming] a cool permutation verb > > I don't see catalog used frequently in natural J code. It does come up on > these Forums from time to time, mostly in contrived situations. In my own > code, I sometimes use it to generate J sentences in order to compare > performance statistics for semantically-equivalent phrases. But outside of > that, I don't see it too often. I suspect one reason for its rarity is, at > least, that in any real-world context, a complete MxN catalog would be > prohibitively expensive. > > So it's unsurprising that APL didn't have a primitive catalog function. Of > course, you could express it as {jot} {dot} {comma}, dot as being outer > product (and jot in this context a placeholder, not unlike [:) with the > usual caveats about the differences between J's rank and APL's > multidimensionality (ie you could expect catalog to work for 1D vectors in > APL and generalized lists in J). > > So, when he got his chance to "rationalize" APL and rebuild it from > the ground up as J, did Ken have a change of heart about catalog's > centrality to the discipline of computer science? Is that why he assigned > to it that scarce and desirable resource, a primitive spelling? A > one-character primitive, no less? > > I suspect not. Recall the other valence of {, to wit: from. You might > think having this kind of partner is an even greater endorsement of > catalog's virtues ... until you realize: > > row_2n3n6_col_7n13 =: 2 3 6 ; 7 13 > table =: i. 10 20 > > (< row_2n3n6_col_7n13) { table NB. "from" > 47 53 > 67 73 > 127 133 > > ({ row_2n3n6_col_7n13) NB. "catalog" > +---+----+ > |2 7|2 13| > +---+----+ > |3 7|3 13| > +---+----+ > |6 7|6 13| > +---+----+ > > ({ row_2n3n6_col_7n13) { table NB. "catalog from" > 47 53 > 67 73 > 127 133 > > Ah, "from" *is* "catalog". Catalog is a primitive because from needed a > thematically related definition for monad { (and from, of course, got a > precious one-character primitive because it *is* central to array > programming). And, incidentally, this is why the results of catalog are > boxed, even though they don't need to be, and we end up writing >@:{ > instead of plain { every time we use it. > > That is, by definition, the results of { will be homogenous in both type > and shape, and so we know for certain boxes aren't required ... except that > dyad { has a scalar left rank, and so to completely address an atom (or > anything more granular than an item, ie a Cartesian point in the frame > specified as a vector of indices, one per axis), each selection must be > boxed. > > True story. > > -Dan > > > > Sent from my iPhone > > > > On May 8, 2014, at 5:34 PM, "'Pascal Jasmin' via Programming" < > [email protected]> wrote: > > > > Its the same. Just more descriptive name than catalogue perhaps. > Google seems to only find J references to query "catalogue function > permutations". I feel as though catalogue and my use of it is a > generalizable pattern, and the J designers agreed, but I don't know if > other languages did something similar, and just used a different name? > > > > Was catalogue in APL? > > > > > > ----- Original Message ----- > > From: David Lambert <[email protected]> > > To: programming <[email protected]> > > Cc: > > Sent: Thursday, May 8, 2014 4:50:40 PM > > Subject: Re: [Jprogramming] a cool permutation verb > > > > Indeed cool, does it differ from ,@{ :[: > >> Date: Thu, 8 May 2014 10:53:53 -0700 (PDT) > >> From: "'Pascal Jasmin' via Programming"<[email protected]> > >> To: Programming forum<[email protected]> > >> Subject: [Jprogramming] a cool permutation verb > >> Message-ID: > >> <[email protected]> > >> Content-Type: text/plain; charset=utf-8 > >> > >> cperm =: [: , [: < "1 [: > [: ,"0 1/ each/ (_2&}. , [: ,"0 0/ each/ > _2&{.) > >> > >> this creates constrained permutations where each position in the list > can only be drawn from its own set: > >> > >> ? ?cperm 3 4 ; 1 2 > >> ????????????????? > >> ?3 1?3 2?4 1?4 2? > >> ????????????????? > >> > >> ? ?cperm 0 ; 3 4 ; 1 2; 5 > >> ????????????????????????????????? > >> ?0 3 1 5?0 3 2 5?0 4 1 5?0 4 2 5? > ---------------------------------------------------------------------- > 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 ---------------------------------------------------------------------- For information about J forums see http://www.jsoftware.com/forums.htm
