Sven,
To me, the keep version would be a lot more readable if it were creating a
literal map in a fn.
I think (for) is almost always the right thing. It's not as fun to write,
but much easier to read:
(for [i (range 1 11)
:let [id (keyword (str "answer_correct_" i))]
:when (params id)]
{:question_id q-id :user_id user-id :answer_id (params id)})
It's possible to shrink the reduce, but I prefer the above.
(reduce
(fn [acc i]
(let [id-correct (->> i (str "answer_correct_) keyword params)]
(cond-> acc id-correct
(conj {:question_id q-id :user_id user-id :answer_id id-correct}))))
[] (range 1 11))
Take care,
Moe
On Tue, Aug 25, 2015 at 9:42 AM, Sven Richter <sver...@googlemail.com>
wrote:
> Hi,
>
> I find myself repeating a certain pattern from time to time.
>
> I have a map like this:
> {:answer_correct_1 2 :answer_correct_3 4 :foo "bar"}
>
> There is a hidden index answer_correct_idx which might range from 1 to x.
> So, what I want is to "iterate" over the map and produce a vec of maps
> given some other fields like this:
> [{:id 123 :answer_correct_1 2} {:id 123 :answer_correct_3 4} ...]
>
> The pattern that I use then is reduce like this:
> (reduce
> (fn [a b]
> (let [id-correct (keyword (str "answer_correct_" b))]
> (if (id-correct params)
> (conj a {:question_id q-id :user_id user-id :answer_id (id-correct
> params)})
> a)))
> [] (range 1 11))
>
> If have an if condition inside the reduce and then either conj or return
> the unchanged vec. This works. But I wondered if there is a higher
> abstraction for it and a very nice guy on slack proposed this:
>
> (let [->id (comp keyword (partial str "answer_correct_"))]
> (map
> (partial hash-map :question_id q-id :user_id user-id :answer_id)
> (keep
> (partial get params)
> (map ->id (range 1 11)))))
>
> It also works, but, regarding readibility I don't think it's easier to get
> (this is subjective of course).
>
> Are there other ways to achieve the same? Maybe something a bit more dense?
>
> Thanks,
> Sven
>
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