Clojure Koans Answers and Explanations - 4 - Sets

After the 3rd Clojure Koans post, this one is for 4th set of Clojure Koans - the one on sets.Unroll your sleeves, this one is a small post.

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;1

(= #{} (set __))

; #{} creates an empty set

; here is another way to do the same thing

(= #{} (set nil))

; do remember to check the type of a set, it is

; user=> (type #{})

; clojure.lang.PersistentHashSet

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;2

(= __ (count #{1 2 3}))

; predictable by now, right?

(= 3 (count #{1 2 3}))

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;3

(= __ (set '(1 1 2 2 3 3 4 4 5 5)))

; a set tries to mirror the set in math

; so, this holds out 

(= (set '(1 2 3 4 5)) (set '(1 1 2 2 3 3 4 4 5 5)))

; and so does

(= #{1 2 3 4 5} (set '(1 1 2 2 3 3 4 4 5 5)))

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;4

(= __ (clojure.set/union #{1 2 3 4} #{2 3 5}))

; as is obvious this asks for invoking union of 2 sets

(= #{1 2 3 4 5} (clojure.set/union #{1 2 3 4} #{2 3 5}))

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;5

(= __ (clojure.set/intersection #{1 2 3 4} #{2 3 5}))

; this one is intersection

(= #{2 3} (clojure.set/intersection #{1 2 3 4} #{2 3 5}))

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;6

(= __ (clojure.set/difference #{1 2 3 4 5} #{2 3 5})))

; a diff of 2 sets is the first set minus the elements

; of 2nd set

(= #{ 1 4} (clojure.set/difference #{1 2 3 4 5} #{2 3 5}))