Futurice training, 5.6.2014

recap.clj

(ns working-with-data
  (:require [working-with-data.data :refer [participants]]))

;; Futu training, 5.6.2014
;; RECAP

(def a {:name "Juho"})

;; assoc - return a new map
(assoc a :age 24)
;; => {:age 24, :name "Juho"}
a
;; => {:name "Juho"}) - this is unchanged

;; dissoc - return a new map
(dissoc a :sdfsdfds)
;; => {:name "Juho"}

;; map - returns a new value for every element of collection
(map :prog-years participants)
;; => (10.0 8.0 4.0 4.0 10.0 10.0 9.0 10.0 11.0 20.0 20.0 5.0 nil 10.0 10.0 15.0 16.0 10.0 15.0 10.0 14.0 15.0)
(filter :scala participants)

;; reduce

;; Ugly version
(reduce (fn [acc p]
          (+ acc (or (:prog-years p) 0)))
        0
        participants
        )

;; Better
(->> participants
     (map :prog-years)
     (remove nil?)
     (reduce +))

;; Pretty
(->> participants
     (keep :prog-years)
     (reduce +))

;; destructuring
;; - head tail second
;; - maps
;; - inner maps

(defn head [[f]]
  f)

(head [1 2 3 4])
;; => 1

(defn second [[_ s]]
  s)

(second [1 2 3 4])
;; => 2

(defn tail [[_ & rest]]
  rest)

(tail [1 2 3 4])
;; => (2 3 4)

(let [{:keys [d] :or {d 1337}} {:a 12 :b 34 :c 42}]
  d)
;; => 1337

(let [[[f] second] [[1 2 3] 4 5 6]]
  {:foo f
   :bar second})
;; => {:foo 1, :bar 4}

(let [{{a :foo} :bar}   {:bar {:foo 5}}]
  a)
;; => 5

(macroexpand-1 '(let [[x y] (f)]))
;; => (let* [vec__3942 (f) x (clojure.core/nth vec__3942 0 nil) y (clojure.core/nth vec__3942 1 nil)])
;; => (let* [vec__3936 col x (clojure.core/nth vec__3936 0 nil) y (clojure.core/nth vec__3936 1 nil)])
;; => (let* [vec__3933 col x (clojure.core/nth vec__3933 0 nil)])

(macroexpand-1 '(let [{a :a} m]))
;; => (let* [map__3939 m map__3939 (if (clojure.core/seq? map__3939) (clojure.lang.PersistentHashMap/create (clojure.core/seq map__3939)) map__3939) a (clojure.core/get map__3939 :a)])

;; A usecase
(fact "echo echos json"
  (let [beer {:beer "olvi" :tags ["oldschool"]}
        {:keys [headers status body]} (post-json "/echo" beer) ;; returns a ring response
        {:strs [content-type]} headers]
    content-type => "image/png"
    status => 200
    body => beer)))