从Clojure中的Collection（地图列表）中获取偶数/奇数索引元素

Question

I have a List of Map, I need to get the even/odd indexed elements from that list in Clojure. I don't want to iterate thought the list with for loop. Is there any small or single_word function?

Answer 1

user=> (take-nth 2 [0 1 2 3 4 5 6 7 8 9])
(0 2 4 6 8)
user=> (take-nth 2 (rest [0 1 2 3 4 5 6 7 8 9]))
(1 3 5 7 9)

Answer 2

I do not know of any built-in function for this, but it is not that verbose to write one yourself, here is my attempt:

(defn evens-and-odds [coll]
  (reduce (fn [result [k v]]
            (update-in result [(if (even? k) :even :odd)] conj v))
          {:even [] :odd []}
          (map-indexed vector coll)))

(evens-and­-odds [ "foo"­ "bar"­ "baz"­ "foob­ar" "quux­" ])
; -> {:even ["foo" "baz" "quux"], :odd ["bar" "foobar"]}