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