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clojurians | clojure | (it's almost 5am here, I'm trying to decide to sleep or to wait) | 2017-12-17T06:53:18.000065 | Berry |
clojurians | clojure | hi!
I'm having trouble with recursion when a function recurs multiple times per call, e.g. when mapping itself over some list
I don't know how to avoid blowing the stack for larger inputs
here's a (over)simplified example, a function which counts the nodes in a tree:
<https://gist.github.com/ihabunek/927e8534bef011dd9c14f0284153e678>
AFAIK, loop/recur is not viable here
any hints would be appreciated. | 2017-12-17T07:01:09.000100 | Elizbeth |
clojurians | clojure | <@Verna>: how do we join the chat ? | 2017-12-17T07:02:05.000067 | Berry |
clojurians | clojure | <@Elizbeth> you can definitely use loop/recur here, but I think you will need an accumulator parameter | 2017-12-17T07:20:49.000006 | Lucio |
clojurians | clojure | ok, i'll give it a shot | 2017-12-17T07:21:35.000023 | Elizbeth |
clojurians | clojure | it will be less sexy than the way you expressed it with recursion though… | 2017-12-17T07:21:59.000026 | Lucio |
clojurians | clojure | as in, it will be less explicit as to what it is doing | 2017-12-17T07:22:11.000058 | Lucio |
clojurians | clojure | but it should get rid of the stack overflow problem if you do it properly | 2017-12-17T07:22:24.000027 | Lucio |
clojurians | clojure | the actual problem is navigating a branching maze, which is similar to the example | 2017-12-17T07:22:39.000030 | Elizbeth |
clojurians | clojure | what about using a stack? | 2017-12-17T07:23:01.000061 | Lucio |
clojurians | clojure | use two exta parameters, an accumulator (integer accumulating the count) | 2017-12-17T07:23:11.000044 | Lucio |
clojurians | clojure | and a stack of things left to explore | 2017-12-17T07:23:16.000027 | Lucio |
clojurians | clojure | basically modelling a breadth first / depth first traversal | 2017-12-17T07:23:31.000049 | Lucio |
clojurians | clojure | there might be std lib functions for that actually, not sure… | 2017-12-17T07:23:39.000058 | Lucio |
clojurians | clojure | not too experienced with B/DFS, will need to explore it a bit before i can answer your question | 2017-12-17T07:24:01.000027 | Elizbeth |
clojurians | clojure | so you could start with an accumulator of 0 and a stack containing only the first node you need to explore | 2017-12-17T07:24:03.000069 | Lucio |
clojurians | clojure | e.g. `[:a]` | 2017-12-17T07:24:07.000039 | Lucio |
clojurians | clojure | stack would contain the ones i have left to explore? | 2017-12-17T07:24:28.000074 | Elizbeth |
clojurians | clojure | as opposed to the ones i have already explored | 2017-12-17T07:24:49.000051 | Elizbeth |
clojurians | clojure | yeah, left to explore | 2017-12-17T07:24:57.000039 | Lucio |
clojurians | clojure | actually, instead of having an accumulator with th count, you could also just flatten the tree to a list | 2017-12-17T07:25:10.000004 | Lucio |
clojurians | clojure | then count the numbr of elements in that list | 2017-12-17T07:25:19.000086 | Lucio |
clojurians | clojure | hang on, I’ll write you an example | 2017-12-17T07:25:29.000068 | Lucio |
clojurians | clojure | ok, the tree is a stupid example :slightly_smiling_face: | 2017-12-17T07:25:30.000019 | Elizbeth |
clojurians | clojure | the stack of things left to explore sounds good for this tree problem, and for mazes which don't have loops | 2017-12-17T07:26:01.000059 | Elizbeth |
clojurians | clojure | if i have loops i guess i'd have to store places already visited | 2017-12-17T07:26:13.000081 | Elizbeth |
clojurians | clojure | yep, if you have loops it’s different :disappointed: | 2017-12-17T07:26:13.000090 | Lucio |
clojurians | clojure | yeah | 2017-12-17T07:26:18.000036 | Lucio |
clojurians | clojure | there might be more optimized algorithms then though, I am not familiar with graph traversal algos | 2017-12-17T07:26:40.000031 | Lucio |
clojurians | clojure | if you were really worried about performance I am sure optimized versions exist | 2017-12-17T07:27:05.000026 | Lucio |
clojurians | clojure | but I think the basic answer to what you were asking is: “use an extra helper function with an ‘accumulator’ parameter, then use recur/loop” | 2017-12-17T07:28:05.000054 | Lucio |
clojurians | clojure | i'm looking at the actual problem i had :smile: | 2017-12-17T07:29:55.000075 | Elizbeth |
clojurians | clojure | trying to apply it | 2017-12-17T07:30:00.000075 | Elizbeth |
clojurians | clojure | but personally I would still use the recursive approach (with stack overflow issues fo large inputs) if I know my inputs will be small | 2017-12-17T07:30:10.000081 | Lucio |
clojurians | clojure | because it’s usually more expressive | 2017-12-17T07:30:16.000098 | Lucio |
clojurians | clojure | at least to me | 2017-12-17T07:30:20.000065 | Lucio |
clojurians | clojure | i like the recursion too | 2017-12-17T07:30:23.000061 | Elizbeth |
clojurians | clojure | i was under the impression that it's not possible to (map recur ...) | 2017-12-17T07:30:38.000019 | Elizbeth |
clojurians | clojure | yeah it’s not possible to do `(map (recur` directly | 2017-12-17T07:30:55.000066 | Lucio |
clojurians | clojure | hang on, I’m writing you an example :slightly_smiling_face: | 2017-12-17T07:31:36.000073 | Lucio |
clojurians | clojure | here's my actual problem, i cleaned it up a bit
<https://github.com/ihabunek/aoc2016/blob/master/src/aoc2016/day17.clj#L53>
this works well when the limit is under several hundred, but the second part of the assignemnt is to find the longest possible path and that's too much | 2017-12-17T07:39:37.000019 | Elizbeth |
clojurians | clojure | <@Elizbeth> <https://repl.it/repls/SaddlebrownLiquidMontanoceratops> | 2017-12-17T07:40:19.000090 | Lucio |
clojurians | clojure | wow cool site | 2017-12-17T07:41:07.000002 | Elizbeth |
clojurians | clojure | for the longest possible path yo might want to take a different approach if the graph is big though | 2017-12-17T07:41:35.000026 | Lucio |
clojurians | clojure | yep | 2017-12-17T07:41:58.000044 | Elizbeth |
clojurians | clojure | and yes <http://repl.it|repl.it> is cool :slightly_smiling_face: | 2017-12-17T07:42:34.000013 | Lucio |
clojurians | clojure | interesting approach, thanks for that example | 2017-12-17T07:42:56.000027 | Elizbeth |
clojurians | clojure | reducing it with set/union, makes sense | 2017-12-17T07:44:03.000071 | Elizbeth |
clojurians | clojure | yeah; actually now that I think of it it’s unecessary if you have a tree structure | 2017-12-17T07:44:44.000034 | Lucio |
clojurians | clojure | since the same node will never appear twice | 2017-12-17T07:44:52.000022 | Lucio |
clojurians | clojure | so you have recur without loop, didn't know that was a thing | 2017-12-17T07:45:02.000013 | Elizbeth |
clojurians | clojure | but if you had a DAG (directed acyclic graph), then that approach would still work | 2017-12-17T07:45:08.000094 | Lucio |
clojurians | clojure | oh hang on | 2017-12-17T07:45:27.000071 | Lucio |
clojurians | clojure | no it wouldn’t it would overcount some nodes… | 2017-12-17T07:45:34.000044 | Lucio |
clojurians | clojure | yes you can recur on the whole function | 2017-12-17T07:45:46.000052 | Lucio |
clojurians | clojure | I think it the doc it says that recur “recurs to a recursion point” | 2017-12-17T07:46:35.000004 | Lucio |
clojurians | clojure | loop introduces a recursion point | 2017-12-17T07:46:40.000017 | Lucio |
clojurians | clojure | but the function itself is also a recursion point | 2017-12-17T07:46:49.000049 | Lucio |
clojurians | clojure | docs can sometimes be a bit terse | 2017-12-17T07:46:51.000002 | Elizbeth |
clojurians | clojure | yes… | 2017-12-17T07:46:55.000036 | Lucio |
clojurians | clojure | makes sense | 2017-12-17T07:46:57.000080 | Elizbeth |
clojurians | clojure | <http://clojuredocs.org|clojuredocs.org> is nice for examples though | 2017-12-17T07:47:10.000059 | Elizbeth |
clojurians | clojure | just for the record: I shouldn’t have used `set` in the example I gave you; at first sight it makes sense, but thinking a bit more about it it doesn’t seem to make sense at all | 2017-12-17T07:49:34.000076 | Lucio |
clojurians | clojure | i usually use a list to preserve order | 2017-12-17T07:50:00.000052 | Elizbeth |
clojurians | clojure | well, it makes some sense, but if you wanted it to behave well on DAGs the function would need to have extra logic to handle already visited nodes | 2017-12-17T07:50:03.000073 | Lucio |
clojurians | clojure | thanks, i think you've steered me in the right direction, i'll play around with it | 2017-12-17T07:51:20.000077 | Elizbeth |
clojurians | clojure | good luck! | 2017-12-17T07:51:30.000056 | Lucio |
clojurians | clojure | next year maybe i'll try racket to get some proper TCO :smile: | 2017-12-17T07:52:09.000027 | Elizbeth |
clojurians | clojure | Please, someone could help me with this:
```
(->> (iota/seq "war-and-peace-full-book.txt")
(r/filter identity)
(r/map (fn [line]
(re-seq #"\w+" line)))
(r/fold (fn
([] 0)
([a line]
(+ a (count line))))))
```
I’m trying this to count words in a file with parallel, that’s Ok with small files but with big txt files. I’m having this problem:
`UnsupportedOperationException count not supported on this type: Long clojure.lang.RT.countFrom (RT.java:664)` | 2017-12-17T08:43:43.000073 | Annemarie |
clojurians | clojure | <@Berry> to join the chat, you need to be logged on Youtube using your google account. | 2017-12-17T08:58:43.000096 | Verna |
clojurians | clojure | sure, `aset` on an object array is constant time. At least as constant as system memory allows (nothing is really constant time in modern hardware). | 2017-12-17T09:53:03.000033 | Sandy |
clojurians | clojure | <@Annemarie> r/fold takes an optional combining function which combines the results of multiple folds; your fold returns a number, if the combine function is not provided, it tries to use your reduce function | 2017-12-17T11:01:34.000086 | Margaret |
clojurians | clojure | <@Annemarie> I think you can just tell it that your combine function is + so change `(r/fold (fn ...))` into `(r/fold + (fn ...))` and that should solve it | 2017-12-17T11:02:12.000077 | Margaret |
clojurians | clojure | <@Annemarie> to be totally clear - it's trying to pass a number to your function because you told it that function could be used to combine the result of multiple folds | 2017-12-17T11:03:24.000004 | Margaret |
clojurians | clojure | also, when you fix it by adding `+` as an arg, your function no longer needs a 0 arity to be defined - only the combining function is called with 0 args | 2017-12-17T11:09:55.000057 | Margaret |
clojurians | clojure | <@Alla> It turned out that I needed to make httpkit understand ring-async | 2017-12-17T11:29:21.000127 | Michelina |
clojurians | clojure | Which requires a tiny wrapper | 2017-12-17T11:29:49.000084 | Michelina |
clojurians | clojure | Hi, Is the Untangled Framework alive or abandoned? | 2017-12-17T13:06:55.000066 | Arnetta |
clojurians | clojure | Is there a way to create an 'array' such that:
1. I can use aset on it
2. it works in cljc (i.e. both clojure and cljs)
3. it lets me store arbitrary object (i.e. not just float or int)
I'm basically looking for 'array of references'
Pre-emptive: why aren't you using a transient! vector? I want real O(1) aset, not O(log_32 n) assoc. | 2017-12-17T13:40:54.000038 | Berry |
clojurians | clojure | `#?(:clj (make-array Object 100) :cljs (make-array js/Object 100))` | 2017-12-17T13:43:15.000005 | Margaret |
clojurians | clojure | `object-array` | 2017-12-17T13:43:26.000004 | Kareen |
clojurians | clojure | oh, that's portable, nice | 2017-12-17T13:43:50.000019 | Margaret |
clojurians | clojure | nice; thanks! | 2017-12-17T13:44:34.000007 | Berry |
clojurians | clojure | <@Michelina> would be nice If the tiny wrappers were available for all. Needed for Aleph & Immutant too. Best would be do PRs to all the servers to have the async? option | 2017-12-17T16:38:57.000064 | Alla |
clojurians | clojure | Agreed. I may take a crack at the advice for httpkit offered here: <https://www.booleanknot.com/blog/2016/07/15/asynchronous-ring.html> | 2017-12-17T16:40:07.000111 | Michelina |
clojurians | clojure | (that's also where i got the tiny wrapper, `ring->httpkit`) | 2017-12-17T16:40:39.000016 | Michelina |
clojurians | clojure | in `plumatic/schema`, is there an option that would allow you to create a condition for a value based on its key in a map? from my understanding it seems that `s/conditional` can only validate the value in which its placed | 2017-12-17T16:51:35.000035 | Ahmad |
clojurians | clojure | consider
```
[{:something1 {:foo 1 :bar 2}}
{:something2 {:span "2" :potato "3"}}]
```
then if the key is `:something1` i'd like to use a certain schema to validate `{:foo 1 :bar 2}` but if the key is `:something2` i'd like to use another schema to validate `{:span "2" :potato "3"}`. | 2017-12-17T16:53:52.000090 | Ahmad |
clojurians | clojure | you can make an s/conditional that looks into the keys | 2017-12-17T17:08:54.000102 | Margaret |
clojurians | clojure | that is, a conditional that says apply schema1 if :something1 is present, otherwise schema2 if :something2 is present, otherwise some default | 2017-12-17T17:09:35.000090 | Margaret |
clojurians | clojure | then schema1 and schema2 have the apropriate maps under those keys | 2017-12-17T17:09:50.000173 | Margaret |
clojurians | clojure | You could also use keys with or, something like (s/keys :req-un [(or :something1 :something2)]) | 2017-12-17T17:47:55.000129 | Daine |
clojurians | clojure | thanks guys, i ended up using <@Margaret>'s tip cuz i'm in a rush here | 2017-12-17T17:58:58.000014 | Ahmad |
clojurians | clojure | <@Daine> is there a keys function in schema? i couldn't find in the docs for the core namespace | 2017-12-17T18:01:19.000014 | Ahmad |
clojurians | clojure | I think <@Daine> was thinking of spec | 2017-12-17T18:15:20.000056 | Margaret |
clojurians | clojure | `(#(reverse (apply vector %&))
:a :b :c)`
is there a way to rewrite the function? (the part before the :a :stuck_out_tongue: :c) | 2017-12-17T20:44:48.000053 | Berry |
clojurians | clojure | `(comp reverse vector)` | 2017-12-17T20:51:05.000010 | Toi |
clojurians | clojure | actually, I think ikt's just #(reverse %&) :slightly_smiling_face: | 2017-12-17T20:51:30.000024 | Berry |
clojurians | clojure | sure | 2017-12-17T20:51:59.000135 | Toi |
clojurians | clojure | ```
(defmacro def-alias [lst]
`(do ~(for [[k v] lst] `(def ~k ~v))))
(macroexpand-1
'(def-alias [[rev reverse] [ki keep-indexed] [pi persistent!] [ti transient] [gi get-in]]))
(comment
(do
((def rev reverse)
(def ki keep-indexed)
(def pi persistent!)
(def ti transient)
(def gi get-in))))
```
what am I doing wrong in this macro? | 2017-12-17T21:11:01.000200 | Berry |
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