clojure.core.async/reduce

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Type: function Added: Clojure unknown Examples: 3 Runnable: 0

([f init ch])

f should be a function of 2 arguments. Returns a channel containing the single result of applying f to init and the first item from the channel, then applying f to that result and the 2^nd item, etc. If the channel closes without yielding items, returns init and f is not called. ch must close before reduce produces a result.

Examples

by jhn on 2015-12-12 . May have evaluation errors. ▶

(require '[clojure.core.async :as async]) ;; some expensive io call (defn expensive-call [m] (Thread/sleep 2000) m) (->> [{:a 1} {:b 2} {:c 3} {:d 4}] (map (fn [m] (async/thread (expensive-call m)))) ; creates a thread per call (async/merge) ; merges the 4 chans returned into 1 (async/reduce merge {}) ; reduces items in chan with merge (async/<!!)) ;;=> {:a 1, :c 3, :b 2, :d 4}

by jhn on 2015-12-12 . May have evaluation errors. ▶

(require '[clojure.core.async :as async]) (def c (async/to-chan (range 10))) (async/<!! (async/reduce + 0 c)) ;;=> 45

by agodde on 2018-06-06 . May have evaluation errors. ▶

(require '[clojure.core.async :as async]) ; define a channel which yields a predefined value after a timeout ; (function 'f' of async/reduce won't be called) (def c (async/reduce f :predefined-value (async/timeout 10000))) (async/<!! c) ; wait 10 seconds ;;=> :predefined-value

See also

• clojure.core.async/merge
• clojure.core.async/map
• clojure.core.async/into

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