Details
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Type:
Enhancement
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Status:
Open
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Priority:
Minor
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Resolution: Unresolved
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Affects Version/s: None
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Fix Version/s: Backlog
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Component/s: None
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Labels:None
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Patch:Code and Test
Description
Reported by H.Duerer, Mar 13, 2009 max-key or min-key will evaluate (k value) multiple times for arguments if more than 2 arguments are passed. This is undesirable if k is expensive to calculate. Something like the code below would avoid these double calculations (at the price of generating more ephemeral garbage) (defn max-key "Returns the x for which (k x), a number, is greatest." ([k x] x) ([k x y] (if (> (k x) (k y)) x y)) ([k x y & more] (second (reduce (fn [x y] (if (> (first x) (first y)) x y)) (map #(vector (k %) %) (cons x (cons y more)))))))
clj-99-min-key-max-key-performance-v1.txt dated Nov 15 2012 changes min-key and max-key to evaluate the function k on each of its other arguments at most once.