If I understand you correctly I am in agreement. I don't think you could take this problem to clojure.core.reducers/reduce or fold because the problem is inherently sequential is it not?
The reduction is basically (intersection (intersection (intersection A B) C) D). I was curious of this myself, how do I abstract out the order of the (reduce set/intersection ...). I couldn't think of one. Breaking this problem out into 'parallel' units of reduction isn't possible because the problem is dependent on order. Which reducers can't have, or so I think after what I have read today. On Friday, January 24, 2014 3:56:23 PM UTC-5, Cedric Greevey wrote: > > An interesting question this raises is if there is any sensible way to > define (intersection). It would need to behave as an identity element for > intersection, so would need to behave as a set (so, (set? (intersection)) > => truthy) that contained everything (so, (contains? (intersection) foo) => > foo no matter what foo is; (partial contains? (intersection)) => identity). > The problem would be what to do with seq? Ideally an infinite seq that will > produce any particular value after finite time would be produced, but > there's no way to sensibly produce "any particular value" given the wide > variety of constructor semantics, builders, factory methods, things not > known to this particular runtime instance but that conceptually exist > somewhere, etc.; of course, the seq return is a dummy of sorts anyway since > you couldn't really use it sensibly to it might as well just return > (range). Printing should likely be overridden to just print > "(intersection)" rather than b0rk the REPL with a neverending stream of > integers (or whatever). > > But then it also subtly violates another property of Clojure set objects: > if (= a b), (not (identical? a b)), and (identical? (a-set a) a), then > (identical? (a-set b) a) and thus (not (identical? (a-set b) b)). The > latter is true under the hypothesis for every "real" set but would be false > for (intersection). > > Perhaps this is why (intersection) is not supported at this time, even > though (union) returns an empty set object, the identity element for the > union operation. > > > On Fri, Jan 24, 2014 at 3:34 PM, Jarrod Swart <jcs...@gmail.com<javascript:> > > wrote: > >> Ah cool, thanks for posting your solution! >> >> On Friday, January 24, 2014 3:29:49 PM UTC-5, Tassilo Horn wrote: >> >>> Jarrod Swart <jcs...@gmail.com> writes: >>> >>> > The reason you can't get this to work is that r/map returns a >>> <reducible> >>> > not a <coll> for reduce to operate on. >>> >>> Ah, indeed. I couldn't see the forest for the trees. >>> >>> > I'm not sure of a solution because I'm not familiar with >>> > core.reducers. >>> >>> This works: >>> >>> (reduce set/intersection (r/foldcat (r/map set [[1 2] [3 1] [1 3]]))) >>> >>> Bye, >>> Tassilo >>> >> -- >> -- >> You received this message because you are subscribed to the Google >> Groups "Clojure" group. >> To post to this group, send email to clo...@googlegroups.com<javascript:> >> Note that posts from new members are moderated - please be patient with >> your first post. >> To unsubscribe from this group, send email to >> clojure+u...@googlegroups.com <javascript:> >> For more options, visit this group at >> http://groups.google.com/group/clojure?hl=en >> --- >> You received this message because you are subscribed to the Google Groups >> "Clojure" group. >> To unsubscribe from this group and stop receiving emails from it, send an >> email to clojure+u...@googlegroups.com <javascript:>. >> For more options, visit https://groups.google.com/groups/opt_out. >> > > -- -- You received this message because you are subscribed to the Google Groups "Clojure" group. To post to this group, send email to clojure@googlegroups.com Note that posts from new members are moderated - please be patient with your first post. To unsubscribe from this group, send email to clojure+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/clojure?hl=en --- You received this message because you are subscribed to the Google Groups "Clojure" group. To unsubscribe from this group and stop receiving emails from it, send an email to clojure+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/groups/opt_out.
