2009/4/22 Michael Wood <esiot...@gmail.com>: > > On Wed, Apr 22, 2009 at 4:57 PM, samppi <rbysam...@gmail.com> wrote: >> >> Let's say I have a sequence of integers: >> (def a (3 9 1 5 102 -322 ...)) >> >> Is there a function for inserting an object—let's say :foo—after >> elements that fulfill a certain predicate? >> Furthermore, I mean inserting :foo after any block of elements that >> fulfill it: >> >> (mystery-function (partial > 6) a) ; -> (3 :foo 9 1 5 :foo 102 >> -322 :foo ...) >> >> Is it possible to do this without a loop? > > This depends on what you mean by "without a loop" I suppose. There > surely has to be a loop somewhere, doesn't there? > > Although there's no explicit loop in Laurent's solution, there is a > (recursive) loop in the definition of partition-by. > > I wasn't sure what you meant by "inserting :foo after any block of > elements that fulfill it", so this was my attempt at a solution: > > (defn insert-right-if [ins coll f] > (cond (empty? coll) coll > (f (first coll)) > (lazy-seq > (cons (first coll) (cons ins (insert-right-if ins (rest coll) f)))) > :else (lazy-seq > (cons (first coll) (insert-right-if ins (rest coll) f))))) > > This will insert ins after every element for which (f element) returns > true, i.e. not quite what you want. > > Laurent's solution breaks with a large sequence: > user=> (take 10 (mystery-function (partial > 6) (iterate inc 0) :foo))
You're right. The use of partition-by here will never the first group. > java.lang.OutOfMemoryError: Java heap space (NO_SOURCE_FILE:0) > user=> (nth (mystery-function (partial > 6) (iterate inc 0) :foo) 100000000) > java.lang.OutOfMemoryError: Java heap space (NO_SOURCE_FILE:0) > > Mine (although it's not quite the right answer) handles this without > running out of memory: > user=> (nth (insert-right-if :foo (iterate inc 0) (partial > 6)) 100000000) > 99999994 > > -- > Michael Wood <esiot...@gmail.com> > > > > --~--~---------~--~----~------------~-------~--~----~ You received this message because you are subscribed to the Google Groups "Clojure" group. To post to this group, send email to clojure@googlegroups.com To unsubscribe from this group, send email to clojure+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/clojure?hl=en -~----------~----~----~----~------~----~------~--~---
