swap keys and values in a map

Question

Is there a function to swap the key and value of a given map. So given a map, I want the keys to become values, and values the keys.

(swap {:a 2 b 4}) => {2 :         


        

Answer 1

Here is an option that may fit the problem using reduce:

(reduce #(assoc %1 (second %2) (first %2)) {} {:a 2 :b 4})

Here in a function

(defn invert [map]
  (reduce #(assoc %1 (second %2) (first %2)) {} map))

Calling

(invert {:a 2 b: 4})

Then there is the reduce-kv (cleaner in my opinion)

(reduce-kv #(assoc %1 %3 %2) {} {:a 2 :b 4})