I've got a collection of unique objects, and I need to partition them into sets. That part's easy enough, but I need to have both of the following be efficient, and preferably easy: - Given an object, determine what set it's in - List all the objects in a given set
In an imperative language this would be fairly simple: create some empty sets, then iterate over all objects; at each step add the object to a set, and adjust the object's "parent" pointer to point at the set it's in. But in a functional, immutable context the circularity involved seems to make this really inconvenient: if I create the set first then it can't point to the object, and if I create the object first it can't point at its set. I could construct all the objects and have a single "global" map, with mappings for both set-id=>[objects] and object=>set-id, but this seems kinda gross and obscures what is actually meant (objects belong to sets) with implementation (integers/keywords mapping to groups of objects, and objects mapping to integers). Likewise, I could use some kind of mutable refs in part of the process, but (a) that feels like giving up, and (b) since I'll be modifying these sets recursively and backtracking to "past" states it would add a tremendous amount of bookkeeping to undo changes. This seems like a pretty common problem, so I'm sure some clever Clojure coder out there has already solved it; what am I missing? -- 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
