Finished sixth koan

This commit is contained in:
Matt Davidson 2022-11-04 22:02:26 +00:00
parent 019aa847cb
commit acdfdcd424
2 changed files with 19 additions and 19 deletions

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@ -7,7 +7,7 @@
(= #{3} (set '(3)))
"Counting them is like counting other collections"
(= 3 (count #{1 2 3}))
(= 3 (count #{1 2 3}))
"Remember that a set is a *mathematical* set"
(= #{1 2 3 4 5} (set '(1 1 2 2 3 3 4 4 5 5)))

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@ -3,60 +3,60 @@
(meditations
"Don't get lost when creating a map"
(= {:a 1 :b 2} (hash-map :a 1 __ __))
(= {:a 1 :b 2} (hash-map :a 1 :b 2))
"A value must be supplied for each key"
(= {:a 1} (hash-map :a __))
(= {:a 1} (hash-map :a 1))
"The size is the number of entries"
(= __ (count {:a 1 :b 2}))
(= 2 (count {:a 1 :b 2}))
"You can look up the value for a given key"
(= __ (get {:a 1 :b 2} :b))
(= 2 (get {:a 1 :b 2} :b))
"Maps can be used as functions to do lookups"
(= __ ({:a 1 :b 2} :a))
(= 1 ({:a 1 :b 2} :a))
"And so can keywords"
(= __ (:a {:a 1 :b 2}))
(= 1 (:a {:a 1 :b 2}))
"But map keys need not be keywords"
(= __ ({2010 "Vancouver" 2014 "Sochi" 2018 "PyeongChang"} 2014))
(= "Sochi" ({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))
(= nil (get {:a 1 :b 2} :c))
"But you can provide your own default"
(= __ (get {:a 1 :b 2} :c :key-not-found))
(= :key-not-found (get {:a 1 :b 2} :c :key-not-found))
"You can find out if a key is present"
(= __ (contains? {:a nil :b nil} :b))
(= true (contains? {:a nil :b nil} :b))
"Or if it is missing"
(= __ (contains? {:a nil :b nil} :c))
(= false (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"))
(= {1 "January" 2 "February"} (assoc {1 "January"} 2 "February"))
"You can also create a new version with an entry removed"
(= {__ __} (dissoc {1 "January" 2 "February"} 2))
(= {1 "January"} (dissoc {1 "January" 2 "February"} 2))
"Create a new map by merging"
(= {:a 1 :b 2 __ __} (merge {:a 1 :b 2} {:c 3}))
(= {:a 1 :b 2 :c 3} (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}))
(= {:a 1 :b 2 :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 __ __ __)
(= (list 2010 2014 2018)
(sort (keys { 2014 "Sochi" 2018 "PyeongChang" 2010 "Vancouver"})))
"You can get the values in a similar way"
(= (list __ __ __)
(= (list "PyeongChang" "Sochi" "Vancouver")
(sort (vals {2010 "Vancouver" 2014 "Sochi" 2018 "PyeongChang"})))
"You can even iterate over the map entries as a seq"
(= {:a __ :b __}
(= {:a 2 :b 3}
(into {}
(map
(fn [[k v]] [k (inc v)])