Is there a standard/library function to transpose a map from key-value to value-keys?
I've met this task many times before, and I'm sure others have too. Here is the code I'm using, mildly highlighted by Google Groups. I used to copy-paste from Pygments.org <http://pygments.org/demo/506245/>, but it seems to no longer work. (defn transpose "Transposes a map of the form k_i -> v_i into v_j -> #{k_j1 k_j2 ...}" [m] (reduce (fn [acc [k v]] (assoc acc v (conj (get acc v #{}) k))) {} m)) (transpose {:a 1 :b 1 :c 2 :d 4 :e 2 :f 1}) ;=> {4 #{:d}, 2 #{:c :e}, 1 #{:a :b :f}} (defn inverse-transpose "Transposes back a map of the form v_i -> #{k_i1 k_12 ...} into k_j -> v_j" [m] (into {} (mapcat (fn [[v ks]] (map #(vector %1 %2) ks (repeat v))) m))) (inverse-transpose (transpose {:a 1 :b 1 :c 2 :d 4 :e 2 :f 1})) ;=> {:d 4, :c 2, :e 2, :a 1, :b 1, :f 1} (let [m {:a 1 :b 1 :c 2 :d 4 :e 2 :f 1}] (= m (inverse-transpose (transpose m)))) ;=> true -- 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.
