在clojure中从数组构建一个hashmap

Question

首先,我是The Iron Yard 12周5中的学生,学习Java后端工程.该课程由大约60%的Java,25%的JavaScript和15%的Clojure组成.

我收到了以下问题(在评论中概述):

;; Given an ArrayList of words, return a HashMap> containing a keys for every
;; word's first letter. The value for the key will be an ArrayList of all
;; words in the list that start with that letter. An empty string has no first
;; letter so don't add a key for it.
(defn index-words [word-list]
  (loop [word (first word-list)
         index {}]
    (if (contains? index (subs word 0 1))
      (assoc index (subs word 0 1) (let [words (index (subs word 0 1))
                                         word word]
                                     (conj words word)))
      (assoc index (subs word 0 1) (conj nil word)))
    (if (empty? word-list)
      index
      (recur (rest word-list) index))))

我能够使用类似的问题,zipmap但我很肯定我错过了这个问题.代码编译但无法运行.

具体来说,我无法在'if'的false子句中更新我的hashmap索引.

我在REPL中测试了这个函数的所有组件,它们是孤立的.但我正在努力把它们放在一起.

供您参考,这是调用word-list的代码.

  (let [word-list ["aardvark" "apple" "zamboni" "phone"]]
    (printf "index-words(%s) -> %s\n" word-list (index-words word-list)))

我希望不是从社区中获得有效的解决方案,而是希望能够让我的大脑朝着正确的方向前进.

Answer 1

该功能assoc不会修改index.您需要使用assoc返回的新值.同样如此conj:它不会修改您传递它的地图.

我希望,这个答案具有你期望得到的性质:只是你问题所在的指针.

顺便说一句:如果你可以做到PersistentList这一点,那么当使用reduce而不是loop和时,它会成为一个单行recur.一个有趣的功能可能是你update-in.

享受Clojure的乐趣.