https://clojurians.slack.com/archives/C03S1KBA2/p1521499148000292

Good problem for this room ^

the asker specified using a particular libary (Joda-Time) but the only library you need nowadays (since 2014) is baked into the JVM (the java.time.* package) You don't even need a "clojure library" to wrap it. But you have to get comfy calling Java objects (really not very different than Ruby or Python)

one way to do it is like so:

(import (java.time LocalDate DayOfWeek))

(let [starting-at (LocalDate/of 2018 3 1)

      days (iterate #(.plusDays % 1) starting-at)

      mondays (filter (fn [day]
                        (= DayOfWeek/MONDAY (.getDayOfWeek day)))
                      days)]
  (str (nth mondays 2)))

nothing gross about mixing Java interop with Clojure sequences

I was just writing it up using clj-time (since the OP asked about Joda Time) and, yeah, I was arriving at the same solution 🙂

(! 770)-> clj -Sdeps '{:deps {clj-time {:mvn/version "RELEASE"}}}'
Clojure 1.9.0
user=> (require '[clj-time.core :as t] '[clj-time.predicates :as p])
nil
user=> (nth (->> (t/date-time 2018 3 1) (iterate #(t/plus % (t/days 1))) (filter p/monday?)) 2)
#object[org.joda.time.DateTime 0x771158fb "2018-03-19T00:00:00.000Z"]
user=> (str *1)
"2018-03-19T00:00:00.000Z"

Or using clojure.java-time (a very thin wrapper for Java Time):

(! 772)-> clj -Sdeps '{:deps {clojure.java-time {:mvn/version "RELEASE"}}}'
Clojure 1.9.0
user=> (require '[java-time :as jt])
nil
user=> (nth (->> (jt/local-date-time 2018 3 1) (iterate #(jt/plus % (jt/days 1))) (filter jt/monday?)) 2)
#object[java.time.LocalDateTime 0x1983b48a "2018-03-19T00:00"]
user=> (str *1)
"2018-03-19T00:00"

@seancorfield I'm mildly surprised that jt/local-date-time takes a 3-argument constructor that only specifies date and not any time.

The underlying constructor in the java library does not offer that arity

hey guys

so, I am trying to remove every new line from a file that I reading using slurp..the way I am trying to remove the new lines is like this: (print (apply str (filter #(not (#{\newline} %)) string))) it words for a small string, but for some reason when I try it over the whole file, it returns something weird, which is pretty much a line in te middle kind of

can anyone see something weird about this function?

@brnbraga95 Since slurp gives you the entire file as a string, a simple string replacement would be a lot more efficient than converting the data to a sequence, filtering it, and squashing it back into a string.

@brnbraga95 So I agree with @seancorfield that something like (.replace string "\n" "") is the way to go, but I'm also not sure why your aren't getting the result you're expecting from your original way. Is it possible there is a carriage return or some other odd character in the file?

it could be that, I indeed changed my approach to read line by line, so that I can work with large files as well

Hi all, can anyone explain to me why commute is called twice? I understand the difference between alter and commute but I don’t know why commute is called at the beginning and at commit point

I'm having some troubles using boot. I've used this guide https://lionfacelemonface.wordpress.com/2015/01/17/boot-getting-started-with-clojure-in-10-minutes/ when I tried to run boot build it said jar has been created, yet I see no jars in my directory

@mailmeupinside not a boot guy myself, but have you looked itno ./target/ dir?

@rauh there's no ./target

it's like boot didn't run at all :thinking_face:

@mailmeupinside boot doesn't write any files by default unless you run the target task afterwards

so boot build target should do the trick

@sundarj it works! thanks a bunch

I have another problem now 😄

(clojure.string/split "foo bar" #" ") ; works
(clojure.string/split ["foo bar" "x y"] #" ") ; obviously doesn't
(apply clojure.string/split ["foo bar" "x y"] #" ") ; also doesn't but I don't know why

apply is for taking the arguments from a collection and applying a function to them, like (apply + [1 2])

ah. I wanted something like Haskell's fmap

=> (apply clojure.string/split ["foo bar" #" "])
["foo" "bar"]

to go "inside" that collection

that's map in Clojure

:face_palm: thanks

@mailmeupinside

=> (map (fn [s] (clojure.string/split s #" ")) ["foo bar" "x y"])
(["foo" "bar"] ["x" "y"])

and if you want all the results in a single collection, use mapcat instead of map

=> (mapcat (fn [s] (clojure.string/split s #" ")) ["foo bar" "x y"])
("foo" "bar" "x" "y")

tysm 🙇 @sundarj

Is there anything like NCruch or Wallaby.js for Clojure? I know there is 'Lein auto test' but is there a plugin were the results appearing withing the editor next to the line with a Green tick or Red cross?

Cursive will do this if you’re using clojure.test

Thanks! Might need to starting using Cursive. Does Cursive have inline evaluation? Does it update the inline evaluation and test as you type?

you can eval expressions in your editor and send them to your repl if that’s what you mean

Yes. That's great thank you.

Could anyone give me a hand finding discrepancy with clob in jdbc? When I run the same query against h2 and posrgresql I get two different results:

(jdbc/query db ["SELECT bar FROM foo"])

({:bar "fapfap"})

({:bar #object[org.h2.jdbc.JdbcClob 0x7844d931 "clob7: 'fapfap'"]})

hey, how do I map three levels deep? 😅 I have something like [[["foo" "bar"]]] and I have to map over foo and bar

it would depend on how invariant that structure/depth is

it is a case of “iterate the most highly nested collection”, or “iterate through the first of the first item”?

((["abcde" "fghij"]) (["abcde" "ecdab"] ["xyz" "ers" "sew"])) would be a sample seq from my code I have to do something for every string

One approach: (map (fn [s] ___) (apply concat (map first input)))

Specter can help:

user=> a
((["abcde" "fghij"]) (["abcde" "ecdab"] ["xyz" "ers" "sew"]))
user=> (transform [ALL ALL ALL] count a)
(([5 5]) ([5 5] [3 3 3]))

oo

I'm doing it in a ->> macro, which complicates stuff a bit 😅

with two levels I could get away with (map #(map seq %) foo) but now it's harder

I think something like specter is going to be necessary if I want it to be any readable

thanks for help 🙂

let's not suggest Specter for beginners

best to learn the fundamentals of the core library

specter is never a necessity, and only sometimes a convenience

Obligatory: “Perhaps you should revisit the data structure?” not-very-helpful suggestion 🙂

also, in this case the answer can't be easier given (def a '((["abcde" "fghij"]) (["abcde" "ecdab"] ["xyz" "ers" "sew"]))) you just (flatten a) ... try (map count (flatten a))

Does anybody know of a library for CLJ/CLJS that has the same intention as How to Design Program's https://docs.racket-lang.org/teachpack/2htdpimage.html ?

oops, didn't realize this was #beginners, in that case specter should wait 🙂

@joelsanchez that can be said about anything that isn't assembly

specter isn't always better in terms of readability, which can't be said when comparing C to assembly

in this example, flatten vs transform [ALL ALL ALL]

they don't do the same thing, so it's not a fair comparison

specter retains the original structure while flatten doesn't

if it's not necessary to do that, the flatten version is of course preferable

that's true, yep

Hi there, does anyone know how I can change javascripts this from cljs? (goog.object/set this "value" "foobar") does not work...

there's this-as and (js-this), you choose

(this-as this
  (goog.object/set this "value" "foobar"))

(goog.object/set (js-this) "value" "foobar")

bear in mind that function literals and partial won't retain this context

Any tips or example projects for building real-time systems with Clojure and PostgreSQL? I am looking to build a realtime app with Clojure and Postgresql using NOTIFY, LISTEN, and UNLISTEN with triggers. I am using the driver here: https://github.com/alaisi/postgres-async-driver

What's the idiomatic way to extract content from deep inside a json object? e.g. { 'results': [ { 'entries': [ { 'features': [ 'a', 'b' ] }, { 'features': ['c', 'd'] ] } ] } <- I'd like to extract 'a', 'b', 'c' and 'd'

(->> (get-in data ["results" 0 "entries"]) (mapcat (fn [entry] (get entry "features")))) => ("a" "b" "c" "d")

@greg316 - thanks - what if there were multiple elements in results? e.g. i didn't want just index 0 or results?

similar idea then - you’d be mapping over (get data "results") instead

right, so you'd nest the maps?

(->> (get data "results") (mapcat (fn [result] (mapcat (fn [entry] (get entry "features")) (get result "entries"))))

ish

or you can nest less and do more pipelining if you prefer

depends on how much context you want to preserve

sorry, but new to this, but by 'more pipelining' do you mean extract some of the nested calls to their own functions?

what do you typically use to construct a data structure? reduce? I want to create a map that would have a letter as a key and how many these letters I've found as a value

that sounds like a reduce to me

although maybe the frequencies function does what you want (it is implemented with reduce)?

https://clojuredocs.org/clojure.core/reduce-kv

thanks 👍

(defn un-frequencies-helper [a-map a-seq]
  (if (empty? a-map)
    (reverse a-seq)
    (let [fst-key ((first a-map) 0)
          fst-val ((first a-map) 1)]
      (if (<= fst-val 1)
        (un-frequencies-helper (rest a-map) (cons fst-val a-seq))
        (un-frequencies-helper (assoc a-map fst-key (dec fst-val))))
      (un-frequencies-helper a-map (cons fst-key a-seq)))))

(defn un-frequencies [a-map]
             (un-frequencies-helper a-map '()))

(un-frequencies {:a 3 :b 2 "^_^" 1})
clojure.lang.ArityException: Wrong number of args (1) passed to: recursion/un-frequencies-helper

hi, where is my error?

@lum you're only passing one argument to un-frequencies-helper here: (un-frequencies-helper (assoc a-map fst-key (dec fst-val)))

ah, fine, thought there was some error with un-frequencies calling the -helper function.

thanks @sundarj

hey guys, I am to print a persistentArrayMap like this: (doseq [[k v] j] (print k)) but I am gettin UnsupportedOperationException nth not supported on this type: PersistentArrayMap clojure.lang.RT.nthFrom (RT.java:983) which I guess means I cant iterate over this kind of data, does anyone know a workaround?

@brnbraga95 call seq on the map.

(although I would have expected doseq to do that for you)

Yes, it does. Just confirmed that. @brnbraga95 can you share a bit more code? What you've written works if j is a hash map literal...

boot.user=> (doseq [[k v] {:a 1 :b 2}] (println k))
:a
:b
nil
boot.user=> (type {:a 1 :b 2})
clojure.lang.PersistentArrayMap

you are totally right. apparently what I got was something called lazySeq that is wrapping some persistentArrayMaps

what I am trying to achieve is am array of jobs ids, types and urgences, which are the values of the persistentMaps, at this point I no longer care for key, which are always new_jobs

Ah, you had a sequence of maps... So you want to produce a sequence of vectors? Like ([<uuid> bills-questions true] [...] [...]) ?

Ideally I would like to have something like:

[
      "690de6bc-163c-4345-bf6f-25dd0c58e864": {
        "type": "bills-questions",
        "urgent": false
      }
]

Since you're starting with a sequence and you want to produce a sequence of the same length, where each element is just a transformation of the original sequence, you want to call map and pass a transformation function:

(map some-function jobs)

That's not a valid data structure -- did you want to produce a hash map, indexed by the job ID? (not a vector)

yes, but I also want to be able to iterate over it, because I want to find workers for those jobs

but I want the smallest payload

If you want to go from a sequence of hash maps to a (new) hash map, then you want reduce.

that is why I am trying to map over and make it a simpler data structure

does not reduce "reduces" it to a single value?

ooh I got you

(reduce (fn [m job] (assoc m ...)) {} jobs)

That will produce a hash map from the jobs. What you assoc into it will be the job ID (as the key) and then a hash map of just the keys you want (as the value).

Is that enough to get you going in the right direction?

yes it is, just to make sure. m is my current hash map (the accumalted), job is the current job I am iterating and {} is a starting hash map

is that correct?