clojure.core/take-while

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Type: function Added: Clojure 1.0 Examples: 5 Runnable: 3

([pred] [pred coll])

Returns a lazy sequence of successive items from coll while (pred item) returns logical true. pred must be free of side-effects. Returns a transducer when no collection is provided.

Examples

by dpritchett on 2010-07-20 ▶

;; Calculate the sum of all numbers under 1000: (reduce + (take-while (partial > 1000) (iterate inc 0))) 499500

by patazj on 2011-11-18 ▶

(take-while neg? [-2 -1 0 1 2 3]) (-2 -1) (take-while neg? [-2 -1 0 -1 -2 3]) ; note: `take-while' stops traversing the collection when the predicate is false, as is different from `filter'. (-2 -1) (take-while neg? [ 0 1 2 3]) () (take-while neg? []) () (take-while neg? nil) ()

by henghuang on 2016-03-15 . May have evaluation errors. ▶

;;take the item while it's included in the set (take-while #{[1 2][3 4]} #{[1 2]}) ([1 2]) (take-while #{[1 2][3 4]} #{[3 4]}) ([3 4]) (take-while #{[1 2][3 4]} #{[4 5]}) () (take-while #{[1 2][3 4]} #{[5 6] [1 2]}); return nil while any item is not included in the set ()

by ibercode on 2018-01-27 ▶

;;take-while practical example (def entries [{:month 1 :val 12} {:month 2 :val 3} {:month 3 :val 32} {:month 4 :val 18} {:month 5 :val 32} {:month 6 :val 62} {:month 7 :val 12} {:month 8 :val 142} {:month 9 :val 52} {:month 10 :val 18} {:month 11 :val 23} {:month 12 :val 56}]) (defn get-result [coll m] (take-while #(<= (:month %) m) coll)) (get-result entries 3) ;;({:m 1, :val 12} {:m 2, :val 3} {:m 3, :val 32})

by cljlc on 2018-10-07 . May have evaluation errors. ▶

;; Note that usually more items are realized than needed. ;; In the example below the first 32 items are calculated, ;; though the first 2 would be enough. ;; This can be especially important when this extra realization ;; leads to an exception (see example at 'take') or requires a lot of ;; resources (CPU, time, memory, etc.) and at the end not needed at all. (let [x (map (fn [i] (println i) (Thread/sleep 100) i) (range 50))] (take-while #(< % 1) x)) 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 (0)

See also

• clojure.core/drop-while (2)
• clojure.core/split-with (1)
• clojure.core/some (15)
• clojure.core/take (3)

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