Add a function to convert a count map to a reversed map.

src/cipher_analytical_machine/analyzers/analyzers.clj

@@ -11,6 +11,16 @@
             (inc (get acc val 0))))
    {} text))
 
+(defn reverse-count-characters
+  "Convert a map of pairs to a map where the characters grouped by the count and a count is the key."
+  [count-map]
+  (reduce
+   (fn [acc [symbol count]]
+     (->> (conj (get acc count []) symbol)
+          (into [])
+          (assoc acc count)))
+   {} count-map))
+
 (defn chi-squared-letter-statistic
   "To calculate the frequency distribution of a letter."
   [letter-count letter-frequence length-text]

test/cipher_analytical_machine/analyzers/analyzers_test.clj

@@ -8,6 +8,13 @@
     (is (= {\a 2 \b 1}
            (count-characters "aba")))))
 
+(deftest reverse-count-characters-test
+  (testing "The symbols must be grouped as a vector and the count must be a key."
+    (are [count-map expected-map]
+        (= expected-map (reverse-count-characters count-map))
+      {\a 1 \b 2 \c 1} {1 [\a \c] 2 [\b]}
+      {\a 1 \b 2 \c 3} {1 [\a] 2 [\b] 3 [\c]})))
+
 (deftest chi-squared-letter-statistic-test
   (testing "If the frequence of A is 0.1, the text length is 100 and contains 20 times, then the chi-squared is 10."
     (is (= 10.0