Javascript地图排序 [英] Javascript Map ordering

问题描述

我最近在我的代码中存在一个错误，这是由于我在查看MDN上的Map对象详细信息时缺少"插入顺序"文本.简而言之，我有一个地图对象，可以说

i recently had a bug in my code that was due to me missing the "in insertion order" text while looking through Map object details on MDN. In short, i have a map object, lets say

let myMap = new Map;

，然后在填充它之后，用简单的 for .. of 语句遍历它的内容.像这样

and then, after populating it, i iterate over its contents with a simple for .. of statement. Like this

for (let [key, val] of myMap) { 
    ...
}

for 循环中的代码取决于要按 key 排序的(键，值)对.但是，填充地图的算法是按照随机顺序进行的(我无法更改).为了解决这个问题，我现在首先将所有可能的键添加到地图对象中，如下所示:

The code in for loop depends on (key, value) pair to be sorted by key. However the algorithm that populates the map, does so in a random order(and i can't change that). To get around this problem, i now add all possible keys to the map object first, something like this:

let myMap = new Map;
for (let i=0; i<maxkey; ++i) myMap.set(key(i), undefined);

// And in the for loop
for (let [key, val] of myMap) {
    if (typeof val === "undefined") continue;
    //...
}

幸运的是，它们并不多(因此性能损失可以忽略不计)，并且这种方法可行.对于我来说，这种解决方案还是有点尴尬.

Fortunately, there aren't many of them(so the performance penalty is negligible), and this works. Still this solution looks a bit awkward to me.

还有更好的东西吗?

推荐答案

地图中键的顺序取决于地图的实现.具有自然排序键的地图通常称为树图，因为这些密钥存储在

The ordering of keys in a map depends on the map implementation. A map with naturally ordered keys is often called a tree map because the keys are stored in a tree. I have not used a tree map in JS so I can't recommend a particular implementation.

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