clojure过滤器嵌套地图以基于内部地图值返回键 [英] clojure filter nested map to return keys based on inner map values

问题描述

对于这个称为表格"的嵌套地图，

For this nested map called "tables",

  (def tables 
   {:tableA {:occupied false :party nil} 
    :tableB {:occupied true :party nil}
    :tableC {:occupied false :party nil}})

如何过滤并获取:occupied = false的键?

how do I filter and get back the keys where :occupied = false ?

正确结果应为(:tableA :tableC)

我可以使用过滤器" HOF来做到这一点吗?我应该使用列表理解吗?

can I do this with "filter" HOF? Should I be using a list comprehension?

推荐答案

使用keep可以很容易地做到这一点:

You could do it pretty easily with keep:

(keep (fn [[k v]] (if-not (:occupied v) k)) tables)

但是，正如您所观察到的，在映射/过滤序列时，尤其是在处理嵌套序列时，使用for通常是一个很好的解决方案.

However, as you observed, using for is often a good solution whenever you're mapping / filtering sequences, especially if you're dealing with nested sequences.

(for [[k v] tables :when (not (:occupied v))] k)

我通常更喜欢使用for，尤其是当我想对目标项目使用解构时.在这种情况下，解构非常适合将键/值对与[k v]绑定.

I usually prefer using for, especially when I want to use destructuring on the target items. In this case, destructuring is nice for binding the key/value pair with [k v].

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