如何在Javascript映射中交换键和值 [英] How to swap Key and Value in Javascript map

问题描述

我有这张ES6地图：

  Map（6）{ Coratia => ; 1，韩国 => ;，挪威 => 2，慕尼黑 => 1，奥地利 => 1，...} 
  

我想交换键和值以使其像这样：

  Map（6）{1 =>  Coratia，1 => 韩国，2 => 挪威，1 => 慕尼黑，1 => 澳大利亚，...} 
  

解决方案

一种使用 CodyKnapp 提到的想法的解决方案。它使用 Array.reduce（）生成 value->密钥反向 Map 。

< pre class = snippet-code-js lang-js prettyprint-override> let myMap = new Map（[[ Cortia，1]，[ Korea，1]，[挪威 ，2]]）; //生成反向Map.let res = [... myMap.entries（）]。reduce（（acc，[k，v]）= >> {acc.has（v）？acc .set（v，acc.get（v）.concat（k））：acc.set（v，[k]）; return acc;}，new Map（））; //记录新生成的Map.res。 forEach（（v，k）=> console.log（`$ {k} => $ {v}`）））;

  .as-console {background-color：black！important; color：lime;}。as-console-wrapper {max-height：100％！important; top：0;}  

注意 ，如评论中所述，您不能有一个地图可以将相同的 key 复制到多个值。

I have this ES6 map:

Map(6) {"Coratia" => 1, "Korea" =>, "Norway" => 2, "Munich" => 1, "Austrlia" => 1, ...}

I'd like to swap the key and values to make it like this:

Map(6) {1 => "Coratia", 1 => "Korea", 2 => "Norway", 1 => "Munich", 1 => "Australia", ...}

解决方案

Here you have one solution that uses the idea mentioned by CodyKnapp. It uses Array.reduce() to generate the value->key reverse Map.

let myMap = new Map([
   ["Cortia", 1],
   ["Korea", 1],
   ["Norway", 2]
]);

// Generate the reverse Map.

let res = [...myMap.entries()].reduce((acc, [k, v]) =>
{
    acc.has(v) ? acc.set(v, acc.get(v).concat(k)) : acc.set(v, [k]);
    return acc;
}, new Map());

// Log the new generated Map.

res.forEach((v, k) => console.log(`${k} => ${v}`));

.as-console {background-color:black !important; color:lime;}
.as-console-wrapper {max-height:100% !important; top:0;}

Note, as mentioned in the commentaries, that you can't have a Map that will duplicate the same key for multiple different values.

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