clojure.core/peek

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Type: function Added: Clojure 1.0 Examples: 4 Runnable: 3

([coll])

For a list or queue, same as first, for a vector, same as, but much more efficient than, last. If the collection is empty, returns nil.

Examples

by pkolloch on 2010-08-20 . May have evaluation errors. ▶

(def large-vec (vec (range 0 10000))) #'user/large-vec (time (last large-vec)) "Elapsed time: 1.279841 msecs" 9999 (time (peek large-vec)) "Elapsed time: 0.049238 msecs" 9999

by TravisHeeter on 2013-11-23 ▶

(peek '(:a :b :c)) :a

by ertugrulcetin on 2016-08-11 ▶

(peek [1 2 3 4]) ;;=> 4 (peek []) ;;=> nil (peek '(1 2 3 4)) ;;=> 1 (peek '()) ;;=> nil (peek nil) ;;=> nil

by ibercode on 2018-02-15 ▶

;;peek on vector returns the last element (peek [1 2 3]) ;; 3 ;;peek on list returns the first element (peek '(1 2 3)) ;; 1

Note by tomby42

Small reminder:

Do not work for arbitrary seq but just for persistent types implementing clojure.lang.IPersistentStack (like clojure.lang.Persistent*).

Example:

user> (peek (cons 1 '()))
; Evaluation aborted.

do not work because type is clojure.lang.Cons but

user> (peek (conj '() 1))
1

works because type is clojure.lang.PersistentList.

See also

• clojure.core/first (2)
• clojure.core/pop (2)
• clojure.core/conj (9)

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