You cannot select more than 25 topics
Topics must start with a letter or number, can include dashes ('-') and can be up to 35 characters long.
64 lines
1.8 KiB
Clojure
64 lines
1.8 KiB
Clojure
(ns koans.06-maps
|
|
(:require [koan-engine.core :refer :all]))
|
|
|
|
(meditations
|
|
"Don't get lost when creating a map"
|
|
(= {:a 1 :b 2} (hash-map :a 1 __ __))
|
|
|
|
"A value must be supplied for each key"
|
|
(= {:a 1} (hash-map :a __))
|
|
|
|
"The size is the number of entries"
|
|
(= __ (count {:a 1 :b 2}))
|
|
|
|
"You can look up the value for a given key"
|
|
(= __ (get {:a 1 :b 2} :b))
|
|
|
|
"Maps can be used as functions to do lookups"
|
|
(= __ ({:a 1 :b 2} :a))
|
|
|
|
"And so can keywords"
|
|
(= __ (:a {:a 1 :b 2}))
|
|
|
|
"But map keys need not be keywords"
|
|
(= __ ({2010 "Vancouver" 2014 "Sochi" 2018 "PyeongChang"} 2014))
|
|
|
|
"You may not be able to find an entry for a key"
|
|
(= __ (get {:a 1 :b 2} :c))
|
|
|
|
"But you can provide your own default"
|
|
(= __ (get {:a 1 :b 2} :c :key-not-found))
|
|
|
|
"You can find out if a key is present"
|
|
(= __ (contains? {:a nil :b nil} :b))
|
|
|
|
"Or if it is missing"
|
|
(= __ (contains? {:a nil :b nil} :c))
|
|
|
|
"Maps are immutable, but you can create a new and improved version"
|
|
(= {1 "January" 2 __} (assoc {1 "January"} 2 "February"))
|
|
|
|
"You can also create a new version with an entry removed"
|
|
(= {__ __} (dissoc {1 "January" 2 "February"} 2))
|
|
|
|
"Create a new map by merging"
|
|
(= {:a 1 :b 2 __ __} (merge {:a 1 :b 2} {:c 3}))
|
|
|
|
"Specify how to handle entries with same keys when merging"
|
|
(= {:a 1 :b __ :c 3} (merge-with + {:a 1 :b 1} {:b 1 :c 3}))
|
|
|
|
"Often you will need to get the keys, but the order is undependable"
|
|
(= (list __ __ __)
|
|
(sort (keys { 2014 "Sochi" 2018 "PyeongChang" 2010 "Vancouver"})))
|
|
|
|
"You can get the values in a similar way"
|
|
(= (list __ __ __)
|
|
(sort (vals {2010 "Vancouver" 2014 "Sochi" 2018 "PyeongChang"}))))
|
|
|
|
"You can even iterate over the map entries as a seq"
|
|
(= {:a __ :b __}
|
|
(into {}
|
|
(map
|
|
(fn [[k v]] [k (inc v)])
|
|
{:a 1 :b 2})))
|