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#specter
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2018-09-03
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unbalanced02:09:39

specific and general question. General question: where does one go to level up in specter? I feel like I've already tapped out on talks/tutorials and I know I'm only scratching the surface. Case in point -- Specific question: given

(def contrived-data {:time 1535940129129
                       :data [{:a [{:start 389
                                    :stop  456}]}
                              {:b [{:start 113
                                    :stop  889}]}]})
I'm attempting to sort by :start. It's blessedly simple to select the values via
(sm/select [:data s/ALL s/MAP-VALS s/ALL :start] contrived-data)
my intuition to do the operation would be
(sm/transform [:data s/ALL s/MAP-VALS s/ALL :start] sort contrived-data)
but I realized my thinking may have gone awry somewhere along the way

nathanmarz02:09:52

@goomba what do you want the result of that transform to be?

unbalanced02:09:24

sorry, should've posted that

unbalanced02:09:42

as in, :b should come first because its :start value is lower

nathanmarz02:09:36

what if the inner collection has multiple :start values?

nathanmarz02:09:43

use the lowest?

unbalanced02:09:12

hadn't thought that far ahead with my contrived example

unbalanced02:09:52

it's the fact that the keys :a and :b "pre-fix" the data makes any sort of normal update-in/`sort-by` completely unusable, at least with any sort of elegance/performance

unbalanced02:09:12

but I encounter this problem all the time

nathanmarz02:09:18

you can use something like (fn [m] (reduce min (traverse [MAP-VALS ALL :start] m)) for a "keyfn" to sort-by

nathanmarz02:09:16

and then (transform :data #(sort-by keyfn %) data)

nathanmarz02:09:55

beware that sort-by will change that vector to a list

unbalanced02:09:15

ohhhh mannn that is cooooolllllll 😄

unbalanced02:09:11

thank you! how did you... well, I guess because you wrote it, I would've thought to use select instead of traverse

nathanmarz02:09:09

always use traverse if all you'll be doing is a reduce over the result

4
nathanmarz02:09:34

more efficient since no intermediate list is materialized

unbalanced02:09:05

🙏 fantastic. Thanks again.