So question.. when you wrap the request as shown here, how does the database handle the open/closing of the connection? Is the connection always open? This is a postgresql database, so it might be my lack of postgresql knowledge, but I was curious what happens to the connection for each user connecting and disconnecting.

I dunno where you are getting that code from, but I wouldn't be surprised if they assume a connection pool

but a lot depends on the value of db, and even what kind of db it is, what library you are using to talk to it

that code tells you almost nothing about it

hey folks, can you tell me if a set can be transformed in vector? if yes, one to achieve it?

i tried with into but does not work

@quieterkali sure!

user=> (vec #{1 2 3})
[1 3 2]

(into [] #{1 2 3}) also works

thank you very much @schmee 🙂

I'm testing out clojure in the repl for the first time

but this gives me java.lang.RuntimeException: No such var: str/starts-with?

I asked a question on stack overflow about rendering comment-trees. maybe if you have a second, take a look, I'd appreciate any help on the topiic ^_^ https://stackoverflow.com/questions/53571904/render-comment-tree-with-rum

@sova recur back to where?

normally the lost of knowledge is handled with accumulators

it's a datastructure just one level deep, but some entries might require the addition of further entries...

{:content "hax" :id 33 :comments [34 35} would pull out 33, 34, and 35, and potentially any comments 34 and 35 have...

accumulators... googles eagerly

hey guys, can i go over set element using reduce? how, please?

@quieterkali 'set element" ?

set values i meant&34547*

oops

set values*

i wanted to use reduce to go through each set values, and perform some oparation and store the result as accumulate avector

vector

I don't know what set values is for, it sounds feasible

ok let's forget about the set

let's say i have a vector [1 2 3 4 5]

iterate through it, using reduce to perform some computing

sure, maybe you do reduce-kv

@quieterkali Maybe just tell what you’re trying to do?

(reduce + 0 [1 2 3 4 5])

sure!

does what you’re saying, but I’m not sure whether that’s helpful to you

want to come up with best way to go over a vector where i will pass each value to a function which will return me another vector, the i will just use conj add the vector to the reduce accumulator

if i am not clear enough let me know please

sounds like a neural net o.O

(reduce fn [] [1 2 3 4 5])

when you say "`conj` add the vector to the reduce accumulator" do you mean the original reduce fxn's accumulator?

yeah exactly

you could have a global atom store the accumulator state, and then toy with it from separate functions

@quieterkali it sounds like you want mapcat

i want to use recuce exactly to not have to use an atom

(mapcat :vals [{:vals [1 2 3]}
               {:vals [4 5 6]}])

=> (1 2 3 4 5 6)

Does that look like it’s going in the right direction?

kind of

the problem is that i don't have those vals yet

i just have a vector which i'll use to get those vals

You can use any function to replace :vals!

(mapcat (fn [i]
          (range i))
        (range 10))
=> (0 0 1 0 1 2 0 1 2 3 0 1 2 3 4 0 1 2 3 4 5 0 1 2 3 4 5 6 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 8)

so take the vector, go through each values of it, retrieve the corresponding vector, then can use mapcat to concat

yes!

that is what i want to acheive

the ideia is collect the list of friends of my friends

and join into a big list that i will use for other computing

ah yeah, I think mapcat is your friend here

@potetm, @sova thank you very much for your help 🙂

is there anyway to find out from code if the code itself is being ran with a specific leiningen profile? the only thing I came up with is to conditionally include a certain source directory, which can add namespaces which you can check for

I have

public abstract class KeyStoreKeyingDataProvider implements KeyingDataProvider
{
    /**
     * Provides a password to load the keystore.
     */
    public interface KeyStorePasswordProvider
    {
        char[] getPassword();
    }

hey guys 🙂 , let's say i have 2 vectors [1 2 4 3 2 5 5 1] and [1 3 4] and want this output [2 2 5 5]

basically take all occurence of one from another. clojure function to achieve that?

off the top of my head, without checking: (remove #(some (fn [x] (= x %)) [1 3 4]) [1 2 4 3 2 5 5 1])

for each element in longer-list, if it exists in smaller-list, remove it, otherwise continue

depending on list size, that’s^ can get crazy inefficient

oh yeah, it's not good lol

Sets to the rescue...

sets wont work

it has dups

Set will remove all duplication, which i don't want

The second list can be a set

The one you are looking up

The first list remains a vector

@potetm exactly 🙂

(remove (set [1 3 4]) [1 2 4 ...])

@cbowdon exactly

oh yeah that did the trick guys

@potetm @nbtheduke @cbowdon thank you very very very much guys

🙂

computational science is mostly sequential math over collections

fair enough @sova

hey guys, it me again, need you to take a lokk to this and tell if there is a better way to acheive the same thing

took it from clojure sorted-map-by documentation

it give follwing output: {5 2, 2 2, 4 1, 3 1}

depends on what you need

i need it to return the map ordered by the values

not by the keys

so i give this {2 2, 4 1, 3 1, 5 2} and give me back {5 2, 2 2, 4 1, 3 1}

(sort-by val
           >
           results)

=> ([2 2] [5 2] [4 1] [3 1])

so it’s a different return type, but what you’re asserting is that you need indexed access as well

(which you already have via your results map)

hunnnn

(sort-by (fn [[k v]]
             [v k])
           (fn [a b]
             (compare b a))
           results)

looks like this is even better

let me check it please

did the trick 🙂

i did a small update to make it look the way i want kkkkkkkk

thank you @potetm

that won’t do what you want!

it happens to be sorted

kkkkkkkkkkkkkkkk

because your list is small

put more than 10 items in your list

hahahahahahahahaha

and it will get un-sorted

i see

the semantics of {} are just k->v

not sort

so what should i do now?

use sorted-map a guess

curious why you need a sorted hashmap as opposed to a hasmap + sorted list of key-values

if that’s really what you need, your original solution is the way to do it

i used frequencies on a vector and i got a map

i need to ordered the map now by the values

and then thank each one in order to look for the corresponding user

Why do you need them ordered? What context do you intend to use them

list of friend suggestion

It seems like at point you don't need it to be a map. You just need to interate through the key value pairs in a sorted order

i am working on friend list suggestion

right so:

(map (fn [[user-id count]]
       (thank-user user-id))
     (sort-by val
              >
              results))

(Maybe better in a doseq. I try to not do side-effects inside a mapping operation.)

so:

(doseq [[user-id count] (sort-by val
                                 >
                                 results)]
  (thank-user user-id))

checking with my problem...

brb

@potetm what thank-user means?

from https://clojurians.slack.com/archives/C053AK3F9/p1543694584100900

I wasn’t sure what you meant, so I just stuck that in there as a placeholder for whatever you want to do w/ each user

oh i see, it could be the function i will call to get the user

right?

yep

I am so happy, I figured out how to nest comments like I was wondering earlier/forever.

^_^

😄

show us how please hahahahaha

Sure thing 😄

data

@potetm @dpsutton @sova thanks for your help 🙂

rum render of data. top half is "no comments for this entry, so print a dead-ended output of its contents, author" bottom half is: there are comments, print the relevant fields and when it gets to "comments" map the render-item function back over the cids you got [in that frame]

example rendering of output in html

my CSS for .padleft is also relevant: it's very brief

indent yo comment tree

So yeah! those 4 images can make a pro comment-tree maker out of anybody ^_^

So something to consider: it’s doing a linear scan for each render-item — (filter ... posts)

You can eliminate that if you store your posts like so:

{77 {:id 77, :contents "" ... }
 33 {:id 33, :contents "" ...}}

so that’ll give you a direct lookup

Neat. hmm

post-id {post-map}

yep

Okay, and how would I alter my code to shortcut that lookup instead of using filter

(get @posts pid) for every filter

But not (:pid @posts)

okay, that's a subtle distinction where you can use (get ..) and the inverted syntaqs don't werk

uuuuh, so

lol

because (pid @posts) would kinda be absurd..

(:pid posts) means you have a map of {:pid {:post “”}}

(pid posts) means pid is a function

Haha! right!

and number aren’t functions in clojure

i'll seven your web app to death

😄

Also: this doesn’t matter so much in cljs, but

when using atoms

you kind of want to start out by saying:

(let [posts @posts] ....)

that way you have the same value of post for the entire function

Ah. and not to dereference multiple times.

or, perhaps even pass in posts

so the function becomes pure

right, it’s a race condition if you do multiple reads

no mud no lotus

cljs is single-threaded and doesn’t interrupt control flow

so it’s not actually an issue for you

but if you went to clojure w/ that, you would have a bad time

Interesting

thank you very much for pointing that out & other points

np!

Here’s a bonus function for indexing by id:

(defn idx-by-id [id-key coll]
  (into {}
        (map (fn [{id id-key :as item}]
               [id item]))
        coll))

so that will make a map that looks like {"77" {:itemzzz...}} ?

yep

Groovy.

call it like (idx-by-id :pid posts)

wow that was painless

in my case :id and @posts

^_^

@potetm you prefrered doseq over map, can you please tell me why?

sequence fns in clojure imply that execution can be lazy

so map, filter, et al

lazy?

when you have side-effects, you usually want to control when you do the side effect

meaning please, see this word a lot, but what it imply i really do't know for sure

sure

so

(do (range)
    :foo)

run that in a repl

did it

😄

returns :foo immediately?

yeah

lazy eval: i only grow coffee beans when i want to drink coffee

Now just run (range)

exaclty

(feel free to cancel execution at any time 🙂)

oooooooooooooooooooooooow

my computer start looking like matrix

kkkkkkkkkkk

what happened is your repl was trying to print the output of (range)

hahahaha

which is infinite

i see

why isn't (matrix) in clojure.core

but the first one, you didn’t use (range) at all

so it didn’t do anything

now when you say (map inc [1 2 3])

the same thing applies

so in the first one range is thet but i didnt use it at all

right?

ah okay

yes, exactly

it creates a sequence, but nothing happens with it

now if you do

(do (map (fn [i]
           (println i)
           (inc i))
         [1 2 3])
    :foo)

nothing gets printed, right?

yeah

whereas:

(map (fn [i]
       (println i)
       (inc i))
     [1 2 3])

nothing

prints things

yeah print

only map, print

so that’s an example of a side effect inside a sequence operation

it probably doesn’t do quite what you want

maybe a better example:

(let [myseq (map (fn [i]
                   (println i)
                   (inc i))
                 [1 2 3])]
  (println "foo"))

it looks like it would print “1 2 3 foo”

but it doesn’t

yeah

hehehehe

only foo nil

(doseq [i (map (fn [i]
                 (inc i))
               [1 2 3])]
  (println i))
(println "foo")

but that does exactly what it looks like it does

because doseq is “eager”

it executes everything immediately

i see now

so, it’s possible to do side effects in sequence operations

and sometimes it works fine

but it’s unnecessarily confusing imo

in terms of what gets executed when

because sequence fns mean “I don’t care when you do this. Just do it whenever.”

and w/ side effects (e.g. looking up users in a db), you generally want to control when that happens

“ok, now that we have all the ids, go get the users in a single call”

it's really interesting

can you provide me some links to dig deep on it

i think i got it, but i would like to make sure of that

and i will come bak to you with more quesstion hehehehehe

http://clojure-doc.org/articles/language/laziness.html looks pretty good

@potetm thank you very muuuch 🙂

yep!

@quieterkali and @sova Since it seems like ya’ll are trying to skill up on clojure, I’d like to mention my stream I started last week: https://www.twitch.tv/timpote

Gonna be doing Advent of Code, but geared toward clojure beginner/intermediates

would love to hear your questions there!

@potetm signing up there hehehehe

M-F @ 12:00 CST

I suppose it would be useful if I mentioned that on Monday I’m planning to cover a lot of clojure topics: imperative vs functional, loop/recur, reduce, transducers

oughta be pretty good 🙂

so on Mondays and Fridays ?

Monday thru Friday

every weekday

ooooooooooooowwwwwwwwwwww

hehehehe

i got it now

setting up my google agenda to not miss them hahahaha

duration 1h, right?

yeah between 30min and 1 hr

Monday will probably be a full hour

cool

okay

What is an idiomatic way of waiting for multiple chans to finish?