clojure.core/sequence

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Type: function Added: Clojure 1.0 Examples: 6 Runnable: 1

([coll] [xform coll] [xform coll & colls])

Coerces coll to a (possibly empty) sequence, if it is not already one. Will not force a lazy seq. (sequence nil) yields (), When a transducer is supplied, returns a lazy sequence of applications of the transform to the items in coll(s), i.e. to the set of first items of each coll, followed by the set of second items in each coll, until any one of the colls is exhausted. Any remaining items in other colls are ignored. The transform should accept number-of-colls arguments

Examples

by yasuto on 2011-06-10 . May have evaluation errors. ▶

(sequence [1 2 3]) (1 2 3) (class (sequence '(1 2 3))) clojure.lang.PersistentList

by G1enY0ung on 2016-10-28 . May have evaluation errors. ▶

;; let us make a transducer (def xf (comp (filter odd?) (take 5))) #'user/xf (sequence xf (range 1 10)) (1 3 5 7 9)

by cljlc on 2018-02-21 . May have evaluation errors. ▶

;; turns a string into a sequence of characters: (sequence "abc") => (\a \b \c)

by phreed on 2018-02-27 . May have evaluation errors. ▶

;; combine a bunch of collections together (sequence cat [[1 2 3] [5 6 7] [8 9 0]]) ;=> (1 2 3 5 6 7 8 9 0) (sequence cat [ '(1 2 3) '(5 6 7) '(8 9 0) ]) ;=> (1 2 3 5 6 7 8 9 0)

by green-coder on 2020-03-27 . May have evaluation errors. ▶

;; When called with multiples collections. (sequence (map vector) [1 2 3] [:a :b :c]) ;=> ([1 :a] [2 :b] [3 :c])

by Crowbrammer on 2021-03-01 ▶

;; Comparison to seq (def v [1 2 3]) (def l '(1 2 3)) (def ss (sorted-set 1 2 3)) (= (seq [1 2 3]) (sequence [1 2 3])) ;;=> true (= (sequence v) (seq v)) ;;=> true (= (sequence l) (seq l)) ;;=> true (= (sequence ss) (seq ss)) ;;=> true ;; Comparison for non-ordered stuff (def m {:a 1 :b 2 :c 3}) (def s #{1 2 3}) (sequence m) ;;=> ([:a 1] [:b 2] [:c 3]) (seq m) ;;=> ([:a 1] [:b 2] [:c 3]) (sequence s) ;;=> (1 3 2) (seq s) ;;=> (1 3 2)

Note by glts

Interesting background about sequence versus eduction: https://groups.google.com/d/msg/clojure/9I6MtgOTD0w/NiG5PimBCP8J

Note by divs1210

Since Clojure's implementation of sequence is in Java, and is pretty involved, I wrote a pure Clojure version to build intuition.

See also

• clojure.core/seq (5)
• clojure.core/eduction (0)

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