在clojure中，如何反转地图层次结构 [英] In clojure, how to reverse a map hierarchy

问题描述

在 clojure ，我有一个地图，包含每一天，每个水果，吃的果实数。我想反转地图的层次结构，并返回相同的数据，但在层次结构顶部的水果。

In clojure, I have a map that contains for each day, and each fruit, the number of fruits eaten. I would like to "reverse the hierarchy" of the map and to return the same data but with the fruits at the top of the hierarchy.

我将通过一个例子：

(map-reverse-hierarchy {:monday {:banana 2 :apple 3} 
                        :tuesday {:banana 5 :orange 2}})
; => {:orange {:tuesday 2},
;     :banana {:tuesday 5, :monday 2},
;     :apple {:monday 3}}

推荐答案

这些片段是从 {k1 {k2 v}}转换而来的到 {k2 {k1 v}} ，然后通过 apply merge-with conj

The pieces are transposed from {k1 {k2 v}}to {k2 {k1 v}} and then merged by apply merge-with conj

(defn map-reverse-hierarchy [mm]
   (apply merge-with conj
     (for [[k1 m] mm [k2 v] m] {k2 {k1 v}})))

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