clojure.core/count

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Type: function Added: Clojure 1.0 Examples: 5 Runnable: 4

([coll])

Returns the number of items in the collection. (count nil) returns 0. Also works on strings, arrays, and Java Collections and Maps

Examples

by MrHus on 2010-07-18 ▶

(count nil) ;;=> 0 (count []) ;;=> 0 (count [1 2 3]) ;;=> 3 (count {:one 1 :two 2}) ;;=> 2 (count [1 \a "string" [1 2] {:foo :bar}]) ;;=> 5 (count "string") ;;=> 6

by rquinn on 2014-01-11 ▶

(count '(1 2 3 3 1)) ;;=> 5 ;; and as a koan (= (count '(1 2 3 3 1)) 5) ;;=> true

by reborg on 2020-01-17 . May have evaluation errors. ▶

;; count can't count beyond (Integer/MAX_VALUE) ;; (in partial compliance with Java's Collection::size() returning int) (count (range (inc (Integer/MAX_VALUE)))) ;; Execution error (ArithmeticException) ;; integer overflow

by JeniferDalcin on 2022-06-28 ▶

(def items-to-buy {:milk 2 :bread 10 :chocolate 1}) (count items-to-buy) ;;=> 3

by aanacarolina on 2024-06-05 ▶

;;be aware that calling count on lazy sequences realizes them (type (map #(println "lazy" %) [1 2 3])) ;clojure.lang.LazySeq (type (count (map #(println "not-lazy-anymore" %) [1 2 3]))) ;not-lazy-anymore 1 ;not-lazy-anymore 2 ;not-lazy-anymore 3 ;java.lang.Integer

See also

• clojure.core/counted? (1)

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