Clojure 获取嵌套映射值 [英] Clojure get nested map value

问题描述

所以我习惯于在我的应用程序中使用嵌套数组或设置映射.我试着像这样在 Clojure 中设置一个:

(def gridSettings{:宽度 50:身高50:ground {:variations 25}:water {:variations 25}})

我想知道您是否知道检索嵌套值的好方法?我试着写

(:variations (:ground gridSettings))

这是可行的，但它是背单词而且相当麻烦，特别是如果我添加几个级别.

解决方案

get-in 就是这样做的:

(进入 gridSettings [:ground :variations])

来自文档字符串:

<块引用>

clojure.core/get-in([m ks] [m ks 未找到])返回嵌套关联结构中的值，其中 ks 是一个键序列.如果键返回 nil不存在，或未找到的值(如果提供).

So I'm used to having a nested array or map of settings in my applications. I tried setting one up in Clojure like this:

(def gridSettings
  {:width 50
   :height 50
   :ground {:variations 25}
   :water {:variations 25}
   })

And I wondered if you know of a good way of retrieving a nested value? I tried writing

(:variations (:ground gridSettings))

Which works, but it's backwords and rather cumbersome, especially if I add a few levels.

解决方案

That's what get-in does:

(get-in gridSettings [:ground :variations])

From the docstring:

clojure.core/get-in
([m ks] [m ks not-found])
  Returns the value in a nested associative structure,
  where ks is a sequence of keys. Returns nil if the key
  is not present, or the not-found value if supplied.

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