导航传染媒介传染媒介对在Clojure的哈希传染媒介

Question

我在2D空间中有一个点矢量,例如:

[[0 0] [1 1] [2 2]]

并且需要计算某个点与向量中每个点之间的距离,以确定向量中的哪个点最接近我正在查询的点.我需要知道距离和最近点,所以我想要一个像这样的哈希矢量:

[{:point [0 0] :dist 2.7} {:point [1 1] :dist 3.5} {:point [2 2] :dist 4.3}]

我如何将前者转变为后者？我试过这样的事情:

(defn closest-point [point all-points]
    (map #({:point % :dist (distance point %)}) all-points))

但是我收到一个错误:

(user=> ArityException Wrong number of args (0) passed to: PersistentArrayMap  clojure.lang.AFn.throwArity (AFn.java:437)

Answer 1

#({...})扩展到(fn [] ({....}))试图调用地图而没有任何参数.

试试这个:

(defn closest-point [point all-points]
    (map (fn [p] {:point p :dist (distance point p)}) all-points))

要么

(defn closest-point [point all-points]
    (map #(hash-map :point % :dist (distance point %)) all-points))

要么

(defn dist-info
  [point p]
  {:point p :dist (distance point p)})

(defn closest-point [point all-points]
    (map #(dist-info point %) all-points))

Answer 2

如果你使用for理解而不是a,这更具可读性map.另外,要实际选择最近的点,您可以使用min-key:

(defn closest-point [point all-points]
  (apply min-key :dist
         (for [p all-points]
           {:point p :dist (distance point p)})))