Hi,
you are using comparator incorrectly. The function you pass there should
return true, when x is to the left of y when called as (f x y). See the
following example.
user=> (defrecord Foo [a b])
user.Foo
; Wrong usage: your example (The new element is always smaller!)
user=> (-> (sorted-set-by (comparator (juxt :a :b))) (conj (Foo. 1 2))
(conj (Foo. 1 3)))
#{#user.Foo{:a 1, :b 3} #user.Foo{:a 1, :b 2}}
user=> (-> (sorted-set-by (comparator (juxt :a :b))) (conj (Foo. 1 2))
(conj (Foo. 1 1)))
#{#user.Foo{:a 1, :b 1} #user.Foo{:a 1, :b 2}}
user=> (-> (sorted-set-by (comparator (juxt :a :b))) (conj (Foo. 1 2))
(conj (Foo. 1 2)))
#{#user.Foo{:a 1, :b 2} #user.Foo{:a 1, :b 2}}
; Correct usage: lexicographic ordering
user=> (-> (sorted-set-by (comparator #(or (< (:a %1) (:a %2)) (< (:b %1)
(:b %2))))) (conj (Foo. 1 2)) (conj (Foo. 1 1)))
#{#user.Foo{:a 1, :b 1} #user.Foo{:a 1, :b 2}}
user=> (-> (sorted-set-by (comparator #(or (< (:a %1) (:a %2)) (< (:b %1)
(:b %2))))) (conj (Foo. 1 2)) (conj (Foo. 1 3)))
#{#user.Foo{:a 1, :b 2} #user.Foo{:a 1, :b 3}}
user=> (-> (sorted-set-by (comparator #(or (< (:a %1) (:a %2)) (< (:b %1)
(:b %2))))) (conj (Foo. 1 2)) (conj (Foo. 1 2)))
#{#user.Foo{:a 1, :b 2}}
HTH.
Meikel
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