如何使用assoc-in更新地图中的多个值？(Clojure)
如何使用assoc-in更新地图中的多个值？(Clojure)
提问于 2018-02-26 19:27:14
我试图更新每一行都有一个“享受-关闭？”这会将真正的“理智-评级”返回到-2 (也就是说，约翰尼的理智评级将更新为-2)。
(def student-database
{ 0 {:enjoy-clojure? false, :name "jimmy",:sanity-rating 9}
1 { :enjoy-clojure? true, :name "johnny",:sanity-rating 2}
2 { :enjoy-clojure? true, :name "jilly",:sanity-rating 5}
3 { :enjoy-clojure? true, :name "janey",:sanity-rating 8}
4 {:enjoy-clojure? false, :name "jelly",:sanity-rating 10}}) 我是Clojure的新手，我尝试过对update和assoc进行研究，但实际上似乎找不到更新多个元素的方法((assoc student-database [0 :sanity-rating] -2)只返回一个元素)。过滤学生数据库取出返回的学生的真实我有
(defn unhinged?
[record]
(:enjoy-clojure? record))
(defn minus-two-students
[student-database]
(filter #(unhinged? %)
(map student-database [0 1 2 3 4])))和回报
({:enjoy-clojure? true, :name "johnny", :sanity-rating 2} {:enjoy-clojure?
true, :name "jilly", :sanity-rating 5} {:enjoy-clojure? true, :name
"janey", :sanity-rating 8})这是很好的工作，但我也需要它来更新他们所有的理智评级为-2。如有任何帮助/建议，将不胜感激。
回答 4
Stack Overflow用户
回答已采纳
发布于 2018-02-27 00:07:56
您没有在您的问题中说您希望函数只返回(= enjoy-clojure? true)记录，但是从您在其他答案中的评论中，我觉得这才是您真正想要的。
所以也许这个？
(defn unhinged?
[record]
(:enjoy-clojure? record))
(defn minus-two-students
[student-database]
(->> student-database
vals
(filter unhinged?)
(map #(assoc % :sanity-rating -2))))输出将
({:enjoy-clojure? true, :name "johnny", :sanity-rating -2}
{:enjoy-clojure? true, :name "jilly", :sanity-rating -2}
{:enjoy-clojure? true, :name "janey", :sanity-rating -2})Stack Overflow用户
发布于 2018-02-26 19:40:22
reduce-kv版本来了！
(defn adjust-sanity [student]
(if (:enjoy-clojure? student)
(assoc student :sanity-rating -2)
student))
(reduce-kv (fn [m k v] (assoc m k (adjust-sanity v)))
{}
student-database)
=>
{0 {:enjoy-clojure? false, :name "jimmy", :sanity-rating 9},
1 {:enjoy-clojure? true, :name "johnny", :sanity-rating -2},
2 {:enjoy-clojure? true, :name "jilly", :sanity-rating -2},
3 {:enjoy-clojure? true, :name "janey", :sanity-rating -2},
4 {:enjoy-clojure? false, :name "jelly", :sanity-rating 10}}或另一个带有帮助函数的选项，用于更新映射的所有值：
(defn update-vals [m f]
(reduce-kv (fn [m' k v] (assoc m' k (f v))) {} m))
(update-vals student-database adjust-sanity)Stack Overflow用户
发布于 2018-02-26 19:40:54
要更新整个db，可以执行以下操作：
(def student-database
{0 {:enjoy-clojure? false, :name "jimmy",:sanity-rating 9}
1 { :enjoy-clojure? true, :name "johnny",:sanity-rating 2}
2 { :enjoy-clojure? true, :name "jilly",:sanity-rating 5}
3 { :enjoy-clojure? true, :name "janey",:sanity-rating 8}
4 {:enjoy-clojure? false, :name "jelly",:sanity-rating 10}})
(defn update-db [db]
(zipmap (keys db)
(map (fn [student]
(cond-> student
(:enjoy-clojure? student)
(assoc :sanity-rating -2)))
(vals db))))
(update-db student-database) ;;=>
{0 {:enjoy-clojure? false, :name "jimmy", :sanity-rating 9},
1 {:enjoy-clojure? true, :name "johnny", :sanity-rating -2} ...}页面原文内容由Stack Overflow提供。腾讯云小微IT领域专用引擎提供翻译支持
原文链接：
https://stackoverflow.com/questions/48995720
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