clojure - 查找嵌套向量中是否存在元素的惯用方法

Question

我已将数据建模为嵌入向量。我需要查找这些向量中是否存在元素。我有下面的代码，它可以正确执行。不过，我想要一些更惯用的方法的建议。

(defn exists-in-vector?
  [my-vec my-sym]
  (= my-sym (first my-vec)))

(defn exists-in-vectors?
  [all-vectors my-symbol]
  (empty? (for [first-vector all-vectors
               second-vector first-vector
               third-vector second-vector
               :when (exists-in-vector? third-vector my-symbol)
               :while (exists-in-vector? third-vector my-symbol)]
           true)))

> (exists-in-vectors? [[[[:a 20] [:b :30]] [[:c 20] [:d :30]]]
                      [[[:h 20] [:g :30]] [[:f 20] [:e :30]]]]
                      :a) => true

Answer 1

这是“扁平化”正是您想要的少数情况之一:

(def vectors [[[[:a 20] [:b :30]] [[:c 20] [:d :30]]] 
             [[[:h 20] [:g :30]] [[:f 20] [:e :30]]]])

(some #{:g} (flatten vectors))
;=> :g

(some #{:k} (flatten vectors))
;=> nil

顺便说一句，展平的定义很有趣。(来源扁平化)或http://clojuredocs.org/clojure_core/clojure.core/flatten :

(defn flatten  "Takes any nested combination of sequential things (lists, vectors,  etc.) and returns their contents as a single, flat sequence.  (flatten nil) returns nil."  {:added "1.2"   :static true}  [x]  (filter (complement sequential?)          (rest (tree-seq sequential? seq x))))