If I understand correctly you don't need an atom to count the elements in a
seq....all you need is 'count'
(let [s [1 2 3 4 5]
n (count s)]
(vector n s))
=> [5 [1 2 3 4 5]]
If you want to count only the first 100 you can first "take" as many as you
need and then count them...you can also use loop/recur if you want to get
down and dirty!
Jim
On Mon, Jul 30, 2012 at 7:30 PM, Vinay D.E <devi...@gmail.com> wrote:
> I am a newbie and was doing some exercises when I ran across something
> that I don't understand.
> I am trying to count the number of elements in an array less than 100.
>
> My first attempt didn't work. The counter returns 0
>
> (let [a (atom 0)
> i (take-while (fn[x] (swap! a inc) (< x 100)) [1 2 3 4 5])]
> [@a i]) => [0 (1 2 3 4 5)]
>
>
> I am not getting any insight from the source
> <http://clojuredocs.org/clojure_core/clojure.core/take-while>of
> 'take-while' too.
> The strange thing is, if I set a break-point, I can see that the atom is
> getting incremented.
>
> (let [a (atom 0)
> i (take-while (fn[x] (swap! a inc) *(swank.core/break) *(< x 100))
> [1 2 3 4 5])]
> [@a i])
>
> whereas if I do this in a slightly more roundabout way, it works!
>
> (let [a (atom 0)
> i (reduce
> (fn[l in]
> (if (or (nil? (last l)) (< (last l) 100))
> ((fn[] (swap! a inc) (conj l in)))
> l )) [] [1 2 3 4 5])]
> [@a i]) => [5 [1 2 3 4 5]]
>
> I tried reading docs, but I am unable to understand what is happening. If
> anyone could please point me in the right direction, it would be great.
> Thanks in advance
> Vinay
>
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