map-invert

;; Despite being in clojure.set, this has nothing to do with sets. 

user=> (map-invert {:a 1, :b 2})
{2 :b, 1 :a}

;; If there are duplicate keys, one is chosen:

user=> (map-invert {:a 1, :b 1})
{1 :b}

;; I suspect it'd be unwise to depend on which key survives the clash.

;; The inverted map of an empty map is also an empty map.
user=> (map-invert {})
{}

;; Using complex values (which serve as keys in the inverted map) is possible.
user=> ((map-invert {:a {:c 5}}) {:c 5})
:a

;; simple text obfuscation and back, with map-invert

(def scramble-key
  {\a \t \b \m \c \o \d \l
   \e \z \f \i \g \b \h \u
   \i \h \j \n \k \s \l \r
   \m \a \n \q \o \d \p \e
   \q \k \r \y \s \f \t \c
   \u \p \v \w \w \x \x \j
   \y \g \z \v \space \space})

(defn scramble [text scramble-key]
  (apply str (map scramble-key text)))

(defn unscramble [text scramble-key]
  (apply str (map (map-invert scramble-key) text)))

(scramble "try to read this if you can" scramble-key)
;; "cyg cd yztl cuhf hi gdp otq"

(unscramble "cyg cd yztl cuhf hi gdp otq" scramble-key)
;; "try to read this if you can"