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datahike
https://datahike.io/, Join the conversation at https://discord.com/invite/kEBzMvb, history for this channel is available at https://clojurians.zulipchat.com/#narrow/stream/180378-slack-archive/topic/datahike
Björn Ebbinghaus 2020-07-19T17:43:22.011200Z
Can anybody help me with a query for a count by two categories? I have a set of opinions. Opinions have the value -1,0 or 1. I want the count of all 1 opinions and the count of all -1 opinions. So far I have:
[:find [(count ?pros) (count ?cons)]
:in $ ?id
:where
[?e ::proposal/id ?id]
[?e ::proposal/opinions ?pros] ; 1
[?pros ::opinion/value 1]) ; 2
[?e ::proposal/opinions ?cons] ; 3
[?cons ::opinion/value -1]))] ; 4?pros and ?cons would be the same, and 2 and 4 would contradict each other.
I think I do not understand or-join enough to say if I have to use it.Björn Ebbinghaus 2020-07-20T15:03:38.022800Z
@ben.sless Thanks a lot! The final query:
(d/q
'[:find (clojure.core/frequencies ?values) .
:where
[?e ::proposal/id]
[?e ::proposal/opinions ?opinions]
[?opinions ::opinion/value ?values]]
@db/conn)clojure.core .
I get:
Execution error (NullPointerException) at datahike.query/-aggregate$fn (query.cljc:907).
null
Ben Sless 2020-07-20T15:13:47.023200Z
to be fair, the datahike docs say you need to provide a fully qualified name. still a gap relative to datomic
Björn Ebbinghaus 2020-07-20T15:17:39.023400Z
Ah. okay. Didn’t see that one.
Ben Sless 2020-07-20T15:23:30.023600Z
Don't feel bad 🙂 custom aggregators aren't something you'd expect to find on the front page
Björn Ebbinghaus 2020-07-19T17:46:23.012500Z
(I like asking questions in Slack because of the personal conversations, but Stack Overflow would be better because other people can find and reference the question later)
Ben Sless 2020-07-19T20:25:51.012600Z
Write your own aggregator which will behave like frequencies?
Ben Sless 2020-07-19T20:29:49.012800Z
for example this is how max aggregator is implemented:
(fn
[coll]
(reduce (fn [acc x]
(if (pos? (compare x acc))
x acc))
(first coll) (next coll)))Ben Sless 2020-07-19T20:30:43.013Z
I think you can even just use frequencies directly