在clojure，如何合并几个映射组合与相同的键到列表中的映射？ [英] In clojure, how to merge several maps combining mappings with same key into a list?

问题描述

在Clojure中，我想将几​​个地图合并为一个地图，将具有相同键值的映射合并成一个列表。

In Clojure, I would like to combine several maps into a single map where mappings with same key are combined into a list.

例如：

{:humor :happy} {:humor :sad} {:humor :happy} {:weather :sunny}

应导致：

{:weather :sunny, :humor (:happy :sad :happy)}

：

(merge-with (comp flatten list) data)

但是效率不高，因为flatten有 O（n）复杂性。

But it is not efficient because flatten has O(n) complexity.

然后我想出了：

(defn agg[x y] (if (coll? x) (cons y x) (list y x)))
(merge-with agg data)

但感觉不到惯用。任何其他想法？

But it feels not idiomatic. Any other idea?

推荐答案

一种方法是

(defn merge-lists [& maps]
  (reduce (fn [m1 m2]
            (reduce (fn [m [k v]]
                      (update-in m [k] (fnil conj []) v))
                    m1, m2))
          {}
          maps))

这有点丑，但是这只是因为你的值不是已经列出的。它还强制所有为列表（因此您会得到：weather [：sunny] ，而不是：weather ：sunny ）。坦率地说，这很可能是你工作的百万分之一。

It's a bit ugly, but that's only because your values aren't already lists. It also forces everything to be a list (so you'd get :weather [:sunny] rather than :weather :sunny). Frankly, this is likely to be a million times easier for you to work with anyway.

如果你已经有每个值作为一个向量，你可以简单地做（apply merge-with into maps）。

If you had each value as a vector already, you could simply do (apply merge-with into maps).

这篇关于在clojure，如何合并几个映射组合与相同的键到列表中的映射？的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！