clojure - 返回序列中的重复项

Question

我能想到的最好的是:

(defn dups [seq]
  (map (fn [[id freq]] id) 
       (filter (fn [[id freq]] (> freq 1))
               (frequencies seq))))

有没有更简洁的方法？

Answer 1

使用列表理解:

(defn dups [seq]
  (for [[id freq] (frequencies seq)  ;; get the frequencies, destructure
        :when (> freq 1)]            ;; this is the filter condition
   id))                              ;; just need the id, not the frequency