On Sun, Apr 3, 2011 at 3:23 AM, Stefan Rohlfing
<[email protected]> wrote:
> @ Ken, Andreas
>
> Thank you for your nice implementations!
>
> As far as I can see, there are two main methods of comparing adjacent items
> of a list:
>
> 1) Take the first item of a coll. Compare the remaining items with an offset
> of 1:
> (map f coll (rest coll))
> ;; apply some sort of filter
>
> 2) Take the first and the second item of a coll. Test if both items exists
> and then compare:
> (let [x (first coll), y (second coll)]
> (and x y (= (f x) (f y))))
>
> The first method works for take-by, but not for drop-while (or so I think).
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.
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