# 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"
:city "Springfield"
:state "IL"}})

; обратимся к вложенному хешу
"IL"

; теперь обновим вложенный хеш

; => {:name "WidgetCo",
; =>           :city "Springfield",

(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? 😶

• Be sure to attach the test output, without it it's almost impossible to figure out what went wrong, even if you show your code. It's complicated for developers to execute code in their heads, but having a mistake before their eyes most probably will be helpful.
In my environment the code works, but not here 🤨

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