clojure - 如何有条件地连接到 clojure 向量

Question

是否有更简洁的方法可以在 clojure 中执行以下操作？

(defn this [x] (* 2 x))
(defn that [x] (inc x))
(defn the-other [x] (-> x this that))

(defn make-vector [thing]
  (let [base (vector (this (:a thing))
                     (that (:b thing)))]
    (if-let [optional (:c thing)]
      (conj base (the-other optional))
      base)))

(make-vector {:a 1, :b 2}) ;=> [2 3]
(make-vector {:a 1, :b 2, :c 3}) ;=> [2 3 7]

我所说的“更清洁”是指更接近这个的东西:

(defn non-working-make-vector [thing]
  (vector (this (:a thing))
          (that (:b thing))
          (if (:c thing) (the-other (:c thing)))))

(non-working-make-vector {:a 1, :b 2} ;=> [2 3 nil]  no nil, please!
(non-working-make-vector {:a 1, :b 2, :c 3} ;=> [2 3 7]

请注意，我可能想在任意键上调用一些任意函数(例如 this、that、the-other) thing 并将结果放入返回的向量中。重要的是，如果映射中不存在该键，则不应在向量中放置 nil 。

这类似于 this question但输出是矢量而不是 map ，因此我无法使用merge。

Answer 1

(defn this [x] (* 2 x))
(defn that [x] (inc x))
(defn the-other [x] (-> x this that))

(def k-f-map {:a this
              :b that
              :c the-other})

(def m1 {:a 1 :b 2})
(def m2 {:a 1 :b 2 :c 3})

(defn make-vector [k-f-map m]
  (reduce (fn [res [fk fv]]
            (if (fk m)
              (conj res (fv (fk m)))
              res))
          [] k-f-map))

(make-vector k-f-map m1)
-> [2 3]

(make-vector k-f-map m2)
-> [2 3 7]