Clojure：如果键存在，惯用更新地图的值 [英] Clojure: idiomatic update a map's value IF the key exists

问题描述

这里是我的问题：我想要一个函数 helpme 获取一个映射并替换键：r code>：g 使用空向量，当且仅当这些键存在。例如：

Here's my problem: I want a function helpme that takes a map and replaces the keys :r and :g with empty vectors if and only if those keys exist. For example:

输入：

(helpme {:a "1" :r ["1" "2" "3"] :g ["4" "5"]})

输出：

{:a "1" :r [] :g []}

---

$ b <

---

Input:

(helpme {:a "1" :r ["1" "2" "3"]})

输出：

{:a "1" :r []}

---

我可以定义一个函数helpme来做到这一点，但它过于复杂，我觉得必须有一个更容易（更习惯）的方式...

---

I can define a function "helpme" that does this, but it's overly complicated, and I feel like there must be an easier (more idiomatic) way...

这里是我做过的过于复杂的方式，如下所示：

Here's the overly complicated way I've done, as requested below:

(defn c [new-doc k] (if (contains? new-doc k) (assoc new-doc k []) new-doc))
(defn helpme [new-doc] (c (c new-doc :r) :g))

推荐答案

(defn helpme [m]
  (into m (for [[k _] (select-keys m [:r :g])]
            [k []])))

短，只需要在一个位置编辑项目数量设置为 [] 更改。

Short, and only requires editing in one place when the number of items to set to [] changes.

这篇关于Clojure：如果键存在，惯用更新地图的值的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！