如何获取序列的倒数第二个元素？克洛尤尔

Question

我知道如何使用函数 Last 获取最后一个元素，但是是否有可能获取序列的倒数第二个元素？

(defn last
  [args]
   (last args))
(last [1 2 3 4]) ;;--> 4 but i want it to return 3

Answer 1

使用reverse、take-last、butlast或nth（这似乎是最快的）：

(defn second-to-last1 [s]
  (second (reverse s)))

(second-to-last1 (range 100))
=> 98

(defn second-to-last2 [s]
  (first (take-last 2 s)))

(second-to-last2 (range 100))
=> 98

(defn second-to-last3 [s]
  (last (butlast s)))

(second-to-last3 (range 100))
=> 98

(defn second-to-last4 [s]
  (nth s (- (count s) 2) nil))

(second-to-last4 (range 100))
=> 98