Can you point me to a working example of one of these structures? On Monday, 18 April 2016 16:30:17 UTC-7, tbc++ wrote: > > And by "fairly common these days", I mean that I run into this sort of > structure a lot in clojure with anything that is trying to logic or query > operations. Probably isn't that common outside of projects in that domain. > > On Mon, Apr 18, 2016 at 5:28 PM, Timothy Baldridge <tbald...@gmail.com > <javascript:>> wrote: > >> assoc-in is defined in terms of assoc: >> https://github.com/clojure/clojure/blob/clojure-1.7.0/src/clj/clojure/core.clj#L5901 >> >> And this structure is fairly common these days, it's basically a index of >> tuples [e a v], and you're creating a eav index and then an av index. >> Datomic does this same sort of thing, for the datom [e a v t] it creates >> indices for :eavt :avet and a few others that escape my memory at the >> moment. >> >> On Mon, Apr 18, 2016 at 5:08 PM, JvJ <kfjwh...@gmail.com <javascript:>> >> wrote: >> >>> I'm implementing a map data structure where most of the values are maps >>> or sets, and these values can be cross-indexed by the keys they contain. I >>> don't know if it already has a name, but I'm calling it a cross-map. It's >>> similar to a two-way map, but they're not the same thing. >>> >>> For instance, a common operation would be something like "give me all >>> values of this map that contain the key :a." >>> >>> In order to do this efficiently, I'm maintaining a second map that maps >>> keys in the values of the main map to keys of the main map whose values >>> contain that key. >>> >>> If that sounds confusing, consider this: >>> main-map: >>> {:foo {:a 1 :b 2} :bar {:a 2 :c 4} :baz {:b 3 :c 5}} >>> >>> Corresponding cross-indices: >>> {:a #{:foo :bar} :b #{:foo :baz} :c #{:bar :baz}} >>> >>> As you can see, each key maintains references to those entries where it >>> is found. >>> >>> When a nested update occurs that adds an entry to one of the main map's >>> values, the efficient thing to do would be to simply conj that new key onto >>> its corresponding cross-index set. >>> >>> However, I am trying to implement this as a clojure IPersistentMap, and >>> the only method I can override is assoc, not assoc-in. >>> >>> Using regular assoc, I would have to compare the old value's keys to the >>> new value's keys and find the set difference of the two, which is not an >>> O(1) operation. >>> >>> Is there any way to override the behaviour of nested associations or >>> updates? >>> >>> Thanks >>> >>> -- >>> 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/d/optout. >>> >> >> >> >> -- >> “One of the main causes of the fall of the Roman Empire was that–lacking >> zero–they had no way to indicate successful termination of their C >> programs.” >> (Robert Firth) >> > > > > -- > “One of the main causes of the fall of the Roman Empire was that–lacking > zero–they had no way to indicate successful termination of their C > programs.” > (Robert Firth) >
-- 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/d/optout.
