count

(count coll)

返回 coll 中元素的数量。

(count nil) 返回 0

coll 也可以是字符串、数组、Java Collection 和 Map 。

user=> (count nil)
0

user=> (count [1 2 3 4])
4

user=> (count (list 1 2 3 4))
4

user=> (count "string")
6

user=> (count {:clojure "Rich" :python "Guido" :ruby :Matz})
3

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