47 lines
1.4 KiB
Clojure
47 lines
1.4 KiB
Clojure
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; "Don't get lost when creating a map"
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(= {:a 1 :b 2} (hash-map :a 1 __ __))
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; "A value must be supplied for each key"
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(= {:a 1} (hash-map :a __))
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; "The size is the number of entries"
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(= __ (count {:a 1 :b 2}))
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; "You can look up the value for a given key"
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(= __ (get {:a 1 :b 2} :b))
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; "Maps can be used as functions to do lookups"
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(= __ ({:a 1 :b 2} :a))
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; "And so can keywords"
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(= __ (:a {:a 1 :b 2}))
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; "But map keys need not be keywords"
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(= __ ({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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(= __ (get {:a 1 :b 2} :c))
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; "But you can provide your own default"
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(= __ (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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(= __ (contains? {:a nil :b nil} :b))
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; "Or if it is missing"
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(= __ (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 __} (assoc {1 "January"} 2 "February"))
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; "You can also create a new version with an entry removed"
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(= {__ __} (dissoc {1 "January" 2 "February"} 2))
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; "Often you will need to get the keys, but the order is undependable"
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(= (list __ __ __)
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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 __ __ __)
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(sort (vals {2010 "Vancouver" 2014 "Sochi" 2018 "PyeongChang"})))
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