Question

如何反转值为序列的地图？在反转映射中，键是所有序列的条目（假设没有重复键）

例如：

(map-invert-tweaked {:monday [:banana :apple]
                     :sunday [:pineapple :mango]}); {:banana :monday
                                                     :apple  :monday
                                                     :pineapple :sunday
                                                     :mango     :sunday}

我希望这个问题定义明确。

Answer 1

你可以使用列表理解。像这样：

(defn map-invert-tweaked [m]
  (into {} (for [[k vs] m
                 v vs]
             [v k])))

这个for部分做了类似的事情：

var result = [];

for (var k in m) {
    var vs = m[k];
    for (var i = 0; i < vs.length; i++) {
        var v = vs[i]
        result.push([v, k]);
    }
}

然后它只是将所有这些对放入地图

在repl中：

user> (map-invert-tweaked {:monday [:banana :apple]
                           :sunday [:pineapple :mango]})
{:banana :monday, :apple :monday, :pineapple :sunday, :mango :sunday}

Answer 2

加入元音一代！

是的，上述方法有效，但使用实际单词作为变量名更容易阅读：

(defn invert-keylist-map [keylist-map]
  (into {} 
    (for [ [curr-key  value-list]   keylist-map
            curr-value              value-list]
      [curr-value curr-key] )))

更好的是使用Prismatic Schema来描述输入和输出的形状。像这样的输出：

(ns ...
  (:require [schema.core :as s] ))

(s/defn invert-keylist-map :- { s/Any s/Any }  ; result is a map of anything -> anything
  [keylist-map  :- { s/Any [s/Any] } ]  ; input is a map of anything -> list-of-anything
  (into {} 
    (for [ [curr-key  value-list]   keylist-map
            curr-value              value-list]
      [curr-value curr-key] )))

map-invert，用于调整值为序列的映射

2 个答案:

加入元音一代！