Hi Stefan,
I am overwhelmed by the 'freedom of choice' Clojure gives you, too. In that
respect it's more like ruby than python.
Nevertheless, I think if you can come up with an algorithm using the built in
functions over sequences like map, reduce, filter, etc.
you should do so.
Either way, it doesn't really matter which way you do it, just do it right and
then refine as you go (and gain more experience).
Just be aware that you have to explicitly loop-recur for tail recursive
processes, recursive processes might blow up your call stack pretty quickly.
So that would cover 1)
For 2)
I can think of a straight forward tail-recursive process to do what you want:
(defn drop-by [f coll]
(loop [coll coll]
(let [x (first coll)
y (second coll)]
(if (and x y (= (f x) (f y)))
(recur (rest coll))
(rest coll)))))
Maybe someone on this list can think of an implementation in terms of sequence
functions.
Cheers
Andreas
P.s. The most powerful tool that comes with Clojure is this community. Use it!
On 03/04/2011, at 5:23 PM, Stefan Rohlfing 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).
>
> Using the second method take-by can be changed into drop-by by only changing
> the last two lines:
>
> (defn drop-by2 [f coll]
> (lazy-seq
> (when-let [s (seq coll)]
> (let [x (first s)
> y (second s)]
> (if (and x y (= (f x) (f y)))
> (drop 2 s)
> (drop 1 s))))))
>
>
> I am curious to know if one of these methods is the preferred way of doing a
> comparison in Clojure (aka Python's one way of doing things). The sheer
> number of possible solutions to the same problem sometimes overwhelms me a
> bit, so that I'm looking for some orientation ;-)
>
> Best regards,
>
> Stefan
>
>
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