Clojure 按值获取映射键 [英] Clojure get map key by value

问题描述

我是一名新的 clojure 程序员.

I'm a new clojure programmer.

鉴于...

{:foo "bar"}

有没有办法检索值为bar"的键名?

Is there a way to retrieve the name of the key with a value "bar"?

我浏览了地图文档，可以看到一种检索键和值或仅检索值而不只是检索键的方法.感谢帮助！

I've looked through the map docs and can see a way to retrieve key and value or just value but not just the key. Help appreciated!

推荐答案

可以有多个值为bar"的键/值对.与它们的键相反，这些值不会被散列用于查找.根据您想要实现的目标，您可以使用如下线性算法查找密钥:

There can be multiple key/value pairs with value "bar". The values are not hashed for lookup, contrarily to their keys. Depending on what you want to achieve, you can look up the key with a linear algorithm like:

(def hm {:foo "bar"})
(keep #(when (= (val %) "bar")
          (key %)) hm)

或

(filter (comp #{"bar"} hm) (keys hm))

或

(reduce-kv (fn [acc k v]
             (if (= v "bar")
               (conj acc k)
               acc))
           #{} hm)

将返回一系列键.如果您知道您的 val 彼此不同，您还可以使用

which will return a seq of keys. If you know that your vals are distinct from each other, you can also create a reverse-lookup hash-map with

(clojure.set/map-invert hm)

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