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Clojure: Еще немного о хешах

В Clojure с помощью хеш-мап очень легко задать полиморфное поведение (есть еще специальный механизм defmulti о нем чуть позже). К тому же, имеется богатая библиотека по обработке коллекций. Рассмотрим еще несколько примеров:

; Создадим простой калькулятор с помощью хеш-мапы
(defn calc [first-num second-num operation]
  (let [operations-map {"+" +
                        "-" -
                        "*" *
                        "^" (fn [a b] (int (Math/pow a b)))}]
  ((operations-map operation) first-num second-num)))

(calc 2 3 "+") ; => 5
(calc 2 3 "-") ; => -1
(calc 2 3 "*") ; => 6
(calc 2 3 "^") ; => 8

; еще немного функций для работы с хешами
(def company
  {:name "WidgetCo"
   :address {:street "123 Main St"
             :city "Springfield"
             :state "IL"}})

; обратимся к вложенному хешу
(get-in company [:address :state])
"IL"

; теперь обновим вложенный хеш
(assoc-in company [:address :street] "303 Broadway")

; => {:name "WidgetCo",
; => :address {:state "IL",
; =>           :city "Springfield",
; =>           :street "303 Broadway"}}

(def scores {"Andrew" 100 "Angela" 200})
(merge scores {"Kim" 150 "Ivan" 200})
; => {"Andrew" 100, "Angela" 200, "Kim" 150, "Ivan" 200}

Instructions

Создайте функцию freq, которая принимает коллекцию элементов и создает хеш-мапу с частотой появления элементов в коллекции. Больше подробностей в примерах.

(freq ["a" "b" "c" "a" "a" "c" "a" "d" "b"])
; => {"a" 4, "b" 2, "c" 2, "d" 1}

(freq [])
; => {}

(freq ["Clojure" "Ruby" "Clojure" "Elixir" "Ruby" "HTML" "JS"])
; => {"Clojure" 2, "Ruby" 2, "Elixir" 1, "HTML" 1, "JS" 1}

(freq [10 10 10 20 300 41 53])
; => {10 3, 20 1, 300 1, 41 1, 53 1}

(freq [:a :b :c :d :a :a])
; => {:a 3, :b 1, :c 1, :d 1}
The exercise doesn't pass checking. What to do? 😶

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In my environment the code works, but not here 🤨

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My code is different from the teacher's one 🤔

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