Clojurians Log v2

God morgen. While working on deps-deploy yesterday, I had to do some RTFSing in pomegranate https://github.com/clj-commons/pomegranate/blob/master/src/main/clojure/cemerick/pomegranate/aether.clj and I'm struck by how different this code is from the code that I write on a day to day basis. From a call-site perspective, kw-args look realy nice:

(aether/deploy :artifact-map artifact-map
                 :repository repository
                 :coordinates coordinates)

What's your preference:

(->> foos (map (fn [foo] [(bar foo) (baz foo)])) (into {}))

(reduce (fn [foos foo] (assoc foos (bar foo) (baz foo))) {} foos)

(into {} (map (juxt bar baz)) foos)

I have a slight preference to put into at the front and yes, juxt, thank you plex!

I'm a big into + map + juxt fan 🙂

Yeah, didn't see the use for juxt here as this was a simplification of a more complex example, but still... Maybe worth thinking how this could be solved with juxt since it probably leads to smaller building blocks

@slipset but there's a law that when you have a chance to use juxt, you should take it. unlike macros

Which law is that? Borkdudes law? 🙂

clj-kondo: warning: this program doesn't use juxt

literally unusable

Is there a way to lint that would suggest juxt, i.e., given the example above?

(I'm still learning when I can use it)

I guess it's something that bikeshed or kibitz could do, since they look at patterns

https://github.com/jonase/kibit

Interesting

So if you can write a pattern that expresses when to use juxt, then you're good.

:thumbsup:

I'm almost always using juxt to turn maps into ordered vectors of the values in maps

And in my example, it gets used to create map entries from vectors so we can stick them in a map

mogge

Oh, I just need to get this off my chest. Wouldn't it be nice if group-by could get an extra arity so you could avoid doing somehting like:

(->> foos
   (group-by :id)
   (medley/map-vals whatever))

(group-by :id whatever foos)

(somewhat inspired by javas grouping collector (or whatever it's called))

Basically this thing here https://github.com/plumatic/plumbing/blob/master/src/plumbing/core.cljx#L164

🐈

I've just gotten really used to writing

(map (fn [[k v]]
  [k (do-sommat-to-v v)])

and just don't use map-vals

grouped-map is a bit different. It looks a bit like by-key from cgrand/xforms

which is perhaps a bit more general as it applies a comped transducer to the groups (does the same for partition)

https://github.com/cgrand/xforms#on-partitioning

@slipset You mean (zipmap (map :id foos) (map whatever foos)) ⛳

Not if whatever removes :id

@slipset I'm confused. What's an example use-case?

Might not be realistic, but let’s try:

(def users [{:age :best, :name "erik"}, {:age :best, :name "dominic"}, {:age :too-old :name "bruce"])
(grouped-map :age :name users)
=> {:best ["erik", "dominic"], :too-old ["bruce"]}     

Oh I see, you want to keep the sequence

@slipset This is just a matter of generalizing group-by right?

(defn group-by2
  [f coll f-combine empty f-elt]
  (persistent!
   (reduce
    (fn [ret x]
      (let [k (f x)]
        (assoc! ret k (f-combine (get ret k empty) (f-elt x)))))
    (transient {}) coll)))
#'user/group-by2

user=> (group-by2 :age users conj [] :name)
{:best ["erik" "dominic"], :too-old ["bruce"]}

You could drop the empty argument and have the combine function defaul accordingly.

(e.g. (fnil conj []) in this case)

you mean like a 0-arg?

yeah

@ordnungswidrig on second thought no, because you can have nil vals:

user=> (get {:a nil} :a :foo)
nil

good point!

hmm, but ret is our own map

so never mind

true

Otoh you can always thread the result of a simple group-by through a combine function

xforms has this, as @otfrom wisely mentioned :)

(->> x (group-by :some-key) (map (fn [[k vs] (reduce + vs)) (into {}))

(Somebody who knows about transducers can rewrite this to be performant I guess)

((But that’s not the point))

there's also index-by from medley which I sometimes need. which can also be written using the very decomplected group-by2:

(def users [{:age :best, :name "erik"}, {:age :best, :name "dominic"}, {:age :too-old :name "bruce"}])

(defn group-by2
  [group-fn combine-fn empty elt-fn coll]
  (persistent!
   (reduce
    (fn [ret x]
      (let [k (group-fn x)]
        (assoc! ret k (combine-fn (get ret k empty) (elt-fn x)))))
    (transient {}) coll)))

(prn (group-by2 :age conj [] :name users))
;;=> {:best ["erik" "dominic"], :too-old ["bruce"]}

(defn index-by [f coll]
  (group-by2 f (fn [_ x] x) nil identity coll))

(prn (index-by :id [{:id 1 :foo 2} {:id 2 :foo 2}]))
;;=> {1 {:id 1, :foo 2}, 2 {:id 2, :foo 2}}

(fn [_ x] x) => second 😛

not really though?

in lambda calculus it's the expression for false I believe

hmmm

actually true!

Tools namespace, why must you bother me so?

I have half a mind to abandon it

TNS-45 has pestered every clojurescript project I've ever been on. As of yet there's no general purpose solution. I'm very tempted to look at alternatives.