clojure.core/last

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Type: function Added: Clojure 1.0 Examples: 5 Runnable: 2

([coll])

Return the last item in coll, in linear time

Examples

by MrHus on 2010-07-18 ▶

(last [1 2 3 4 5]) 5 (last ["a" "b" "c" "d" "e"]) "e" (last {:one 1 :two 2 :three 3}) [:three 3] (last []) nil ;; but be careful with what you expect from a map (or set): (last {:a 1 :b 2 :c 3 :d 4 :e 5 :f 6 :g 7 :h 8 :i 9}) [:a 1]

by boxie on 2010-11-06 ▶

;really slow reverse ;put the last item of the list at the start of a new list, and recur over all but the last item of the list. ;butlast acts similar to next in that it returns null for a 1-item list. (defn my-reverse ([a-list] (cond (= a-list nil) nil :else (cons (last a-list) (my-reverse (butlast a-list))))))

by webappzero on 2017-07-13 . May have evaluation errors. ▶

;; Prefer clojure.core/peek over `last` for potentially large vectors. (def v (into [] (take 900900 (range)))) #'user/v (time (last v)) "Elapsed time: 24.460958 msecs" 900899 (def v2 (into [] (take 900900 (range)))) #'user/v2 (time (peek v2)) "Elapsed time: 0.020498 msecs" 900899 ;; For a deep dive into why Rich Hickey chose not to make `last` performant ;; for large vectors, please see: ;; https://gist.github.com/reborg/dc8b0c96c397a56668905e2767fd697f

by tomdl89 on 2023-03-30 . May have evaluation errors. ▶

;; last is also inefficient for sorted-sets and sorted-maps, and ;; peek doesn't work for these, so we can combine `first` with `rseq` ;; to efficiently get the last element on large sorted- collections instead (def sm (into (sorted-map) (map vector (range 1e6) (repeatedly #(rand-int 100))))) (time (last sm)) "Elapsed time: 144.298867 msecs" ;; => [999999 42] (time (first (rseq sm))) "Elapsed time: 0.024408 msecs" ;; => [999999 42]

by sanel on 2024-10-11 . May have evaluation errors. ▶

;; Beside using clojure.core/peek for fast access to the last element in ;; a large vector, you can also use (first (rseq)) which is performant as well (def v (into [] (take 900900 (range)))) (time (last v)) "Elapsed time: 24.825208 msecs" 900899 (def v2 (into [] (take 900900 (range)))) (time (peek v2)) "Elapsed time: 0.02343 msecs" 900899 (def v3 (into [] (take 900900 (range)))) (time (first (rseq v3))) "Elapsed time: 0.02581 msecs" 900899

See also

• clojure.core/first (2)
• clojure.core/next (2)
• clojure.core/rest (6)
• clojure.core/butlast (4)
• clojure.core/take-last (1)
• clojure.core/peek (3)

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