Clojure压缩向量

我会这样写:

(ns ...
  (:require [clojure.contrib.seq-utils :as seq-utils]))

(defn compress-vec
  "Returns a list containing a boolean value indicating whether the
  vector was changed, and a vector with all the nils in the given
  vector shifted to the beginning."
  ([v]
     (let [shifted (vec (apply concat (seq-utils/separate nil? v)))]
       (list (not= v shifted)
             shifted))))

编辑:所以,和托马斯打我的帖子一样,但我不会使用flatten,以防你最终使用某种seqable对象来表示珠宝。

也许这样:

(defn shift-nils-left
   "separate nil values" 
    [s] 
    (let [s1 (vec (flatten (clojure.contrib.seq/separate nil? s)))] 
        (list (not (= s s1)) s1)))

nil? 和 (complenent nil?) ). 这个 not= 在无移位的最坏情况下第三次遍历输入。

(defn compress-vec
  [v]
  (let [[shift? nils non-nils]
        (reduce (fn [[shift? nils non-nils] x]
                  (if (nil? x)
                    [(pos? (count non-nils)) (conj nils nil) non-nils]
                    [shift? nils (conj non-nils x)]))
                [false [] []] v)]
    [shift? (into nils non-nils)]))

(def v [1 2 nil 4 5 nil 7 8] )

(apply vector (take 8 (concat (filter identity v) (repeat nil))))

这将使用 filter take 8 确保向量大小正确。