(count coll)
Returns the number of items in the collection. (count nil) returns 0. Also works on strings, arrays, and Java Collections and Maps
(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
(count '(1 2 3 3 1))
;;=> 5
;; and as a koan
(= (count '(1 2 3 3 1)) 5)
;;=> true