clojure.set/map-invert is the closest I can think of in the functions included with Clojure to your transpose function, but it does not handle duplicate values the way your transpose does.
Andy On Fri, Aug 1, 2014 at 11:16 AM, Bruno Kim Medeiros Cesar < brunokim...@gmail.com> wrote: > 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. > -- 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.
