On Sun, Apr 3, 2011 at 7:15 AM, Meikel Brandmeyer <m...@kotka.de> wrote: > Hi, > > On 3 Apr., 12:24, Ken Wesson <kwess...@gmail.com> wrote: > >> I don't. :) >> >> (defn drop-by [f coll] >> (let [fs (map f coll) >> ps (map = fs (rest fs)) >> zs (map list ps (rest coll))] >> (map second (drop-while first zs)))) >> >> user=> (drop-by #(mod % 3) [1 4 1 7 34 16 10 2 99 103 42]) >> (2 99 103 42) >> >> I especially like the symmetry of using take-while for the one and >> drop-while for the other, under the hood. > > Or a bit less involved. > > (defn take-by > [f coll] > (lazy-seq > (when-let [s (seq coll)] > (let [fst (first s) > value (f fst)] > (cons fst (take-while #(-> % f (= value)) (rest s))))))) > > (defn drop-by > [f coll] > (lazy-seq > (when-let [s (seq coll)] > (let [fst (first s) > value (f fst)] > (drop-while #(-> % f (= value)) (rest s))))))
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