Hi Moe,
Thanks, i didn't know about :when and :let in for. That is my favorite so
far, small and readable, looks good.
Sven
Am Dienstag, 25. August 2015 11:17:23 UTC+2 schrieb Moe Aboulkheir:
>
> 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 <sve...@googlemail.com
> <javascript:>> 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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