http://dev.clojure.org/jira This file is an XML representation of an issue en-us 4.4 649 25-07-2011 http://dev.clojure.org/jira/browse/CLJ-99 Clojure <div class="code panel" style="border-width: 1px;"><div class="codeContent panelContent"> <pre class="code-java">Reported by H.Duerer, Mar 13, 2009 max-key or min-key will evaluate (k value) multiple times <span class="code-keyword">for</span> arguments <span class="code-keyword">if</span> more than 2 arguments are passed. This is undesirable <span class="code-keyword">if</span> k is expensive to calculate. Something like the code below would avoid these <span class="code-object">double</span> calculations (at the price of generating more ephemeral garbage) (defn max-key <span class="code-quote">"Returns the x <span class="code-keyword">for</span> which (k x), a number, is greatest."</span> ([k x] x) ([k x y] (<span class="code-keyword">if</span> (&gt; (k x) (k y)) x y)) ([k x y &amp; more] (second (reduce (fn [x y] (<span class="code-keyword">if</span> (&gt; (first x) (first y)) x y)) (map #(vector (k %) %) (cons x (cons y more)))))))</pre> </div></div> CLJ-99

GC Issue 95: max-key and min-key evaluate k multiple times for arguments

Enhancement Minor Open Unresolved Unassigned Andy Fingerhut Wed, 17 Jun 2009 15:49:00 -0500 Thu, 15 Nov 2012 21:36:54 -0600 Backlog 0 1 <p>Converted from <a href="http://www.assembla.com/spaces/clojure/tickets/99">http://www.assembla.com/spaces/clojure/tickets/99</a></p> <p>richhickey said: Updating tickets (#8, #19, #30, #31, #126, #17, #42, #47, #50, #61, #64, #69, #71, #77, #79, #84, #87, #89, #96, #99, #103, #107, #112, #113, #114, #115, #118, #119, #121, #122, #124)</p> <p>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.</p> Global Rank Patch Code and Test