JavaScript：类映射数组、排序和添加

JavaScript: Map-Like Array, Sorting and Adding

提问by felix_xiao

I'm trying to create a map or dictionary style data structure in JavaScript. Each string key points to an array of int, and I'd like to do a few simple things with the arrays that the keys point to.

我正在尝试在 JavaScript 中创建地图或字典样式的数据结构。每个字符串键都指向一个 int 数组，我想对键指向的数组做一些简单的事情。

I have a bunch of animals, each with an ID (1,2,3,...). I want to put these in a map so I know that 1,4,5 are cats and that 2,3,6 are dogs.

我有一堆动物，每个动物都有一个 ID（1,2,3,...）。我想把这些放在地图上，所以我知道 1,4,5 是猫，2,3,6 是狗。

Here's what I have for code to explain it better.

这是我可以更好地解释它的代码。

var myMap = {};
myMap["cats"] = new Array(1,4,5);   //animals 1,4,5 are cats
myMap["dogs"] = new Array(2,3,6);   //animals 2,3,6 are dogs  

1) How would I add something to an array? For example, if animal #7 is a cat, would the following code be correct?

1）如何向数组中添加内容？例如，如果动物 #7 是一只猫，那么下面的代码是否正确？

myMap["cats"].push(7);   //so that myMap["cats"] is now an array with [1,4,5,7]

2) How would I sort the map so that the keys are ordered by the number of items in their arrays? In this case, myMap["cats"] would be in front of myMap["dogs"] because the array for "cats" has more items than the array for "dogs". Would the following code be correct?

2）我将如何对地图进行排序，以便键按数组中的项目数排序？在这种情况下，myMap["cats"] 将在 myMap["dogs"] 前面，因为“cats”的数组比“dogs”的数组有更多的项目。以下代码是否正确？

myMap.sort(function(a,b){return myMap[b].length - myMap[a].length});

If there's a much more efficient way to do this in JavaScript, please let me know. Thank you so much!

如果在 JavaScript 中有更有效的方法可以做到这一点，请告诉我。太感谢了！

回答by

Seems you've answered your own first question.

似乎您已经回答了自己的第一个问题。

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As for the second question, you'll need another Array to maintain a sort order of the map keys.

至于第二个问题，您需要另一个 Array 来维护映射键的排序顺序。

var mapKeys = Object.keys(myMap);

mapKeys.sort(function(a,b){return myMap[b].length - myMap[a].length});

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Then you can iterate the mapKeysto obtain the collections in your sorted order.

然后，您可以迭代mapKeys以按排序顺序获取集合。

mapKeys.forEach(function(key) {
    console.log("Processing ", key);
    var indices = myMap[key];
});

回答by Sean Vieira

1) Yes, pushwould work (as would unshiftor splice).

1) 是的，push会起作用（就像unshift或 一样splice）。

2) Object keys are inherently unordered and as such they do not have a sortfunction :-) You could add a function to your map to return the values in sorted order however:

2）对象键本质上是无序的，因此它们没有sort函数:-)您可以向地图添加一个函数以按排序顺序返回值：

myMap.sort = function sortMap(sortFunc) {
    var results = [];
    for (key in this) {
        if (this.hasOwnProperty(key) && this[key] !== sortMap) {
            results.push(this[key]);
        }
    }
    return results.sort(sortFunc);
};

myMap.sort(function(a, b) { return a.length - b.length; });

Some notes:

一些注意事项：

• Don't use Arrayor new Arrayunless you need to (e. g. Array(12).join("-")to create a string of 11 dashes). Instead use the array literal syntax []. It's clearer (and in most browsers actually faster).
• When in doubt, open up MDN and the console in your browser and try it out.

• 不要使用Array或new Array除非您需要（例如Array(12).join("-")创建一个由 11 个破折号组成的字符串）。而是使用数组文字语法[]。它更清晰（并且在大多数浏览器中实际上更快）。
• 如有疑问，请在浏览器中打开 MDN 和控制台并尝试一下。

回答by ruakh

How would I sort the map so that the keys are ordered by the number of items in their arrays?

我将如何对地图进行排序，以便键按数组中的项目数排序？

Maps are not ordered — there is no difference between { 'cats': [1,4,5], 'dogs': [2,3,6] }and { 'dogs': [2,3,6], 'cats': [1,4,5] }.

地图是无序的——{ 'cats': [1,4,5], 'dogs': [2,3,6] }和之间没有区别{ 'dogs': [2,3,6], 'cats': [1,4,5] }。

As for the rest of your question — yes, that's all correct. But instead of writing this:

至于你的其余问题——是的，都是正确的。但不是写这个：

var myMap = {};
myMap["cats"] = new Array(1,4,5);   //animals 1,4,5 are cats
myMap["dogs"] = new Array(2,3,6);   //animals 2,3,6 are dogs  

I'd recommend writing this:

我建议写这个：

var myMap = {
    'cats': [1,4,5], //animals 1,4,5 are cats
    'dogs': [2,3,6]  //animals 2,3,6 are dogs  
};

or perhaps this:

或者这个：

var animals = [ 'cats', 'dogs', 'dogs', 'cats', 'cats', 'dogs' ];