Clojure按值获取映射关键字 [英] Clojure get map key by value

问题描述

我是一个新的clojure程序员。

I'm a new clojure programmer.

给定...

{:foo "bar"}

是否有办法检索键和值bar？

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

我浏览了地图docs，可以看到一种方式来检索键和值或只是值，但不只是键。帮助赞赏！

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

可以有多个键/值对，值为bar。这些值不是用于查找的哈希，与它们的键相反。根据你想要实现什么，你可以用一个线性算法来查找键：

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)

这将返回一系列键。如果你知道你的val是彼此不同，你也可以创建一个反向查找哈希映射与

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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