如何在 JavaScript 中创建双向映射，或以其他方式交换值？
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How can I create a two-way mapping in JavaScript, or some other way to swap out values?
提问by Doorknob
I currently have a need to temporarily swap out values in a JavaScript string, and therefore I will need to have a two-way map/hash thing.
我目前需要临时交换 JavaScript 字符串中的值，因此我需要有一个双向映射/哈希的东西。
For example, let's say I want to change \*to __asterisk__(this is just an example, it's not what I'm actually trying to do). I'll have to be able to map *to __asterisk__(to swap out the value in the original string), but then I'll also have to be able to map __asterisk__back to *(to get the original string back).
例如，假设我想更改\*为__asterisk__（这只是一个示例，这不是我真正想要做的）。我必须能够映射*到__asterisk__（以换出原始字符串中的值），但是我还必须能够映射__asterisk__回*（以取回原始字符串）。
Here's some quick pseudo-ish code of the kind of thing that I'm looking for, so you can understand it better:
这是我正在寻找的那种东西的一些快速伪代码，所以你可以更好地理解它：
var myString = 'this is \* a test';
// ???
var twoWayMap = new TwoWayMap('*' <---> '__asterisk__', '%' <---> '__percent__', ...);
var newString = myString.replace(/\(.)/g, function(m, c) {
return twoWayMap.getKey(c);
});
// newString is now 'this is __asterisk__ a test'
// ... later in the code ...
var oldString = newString.replace(/__([^_]+)__/g, function(m, c) {
return twoWayMap.getValue(c);
});
// oldString is now 'this is * a test'
This is what I've thought about and tried so far:
这是我迄今为止所想和尝试过的：
var twoWayMap = {'*': '__asterisk__', '%': '__percent__', ...};
// getKey would be like this:
twoWayMap[c];
// getValue would be like:
var val; for (var x in twoWayMap) { if (twoWayMap[x] === c) { val = x; break } }
The obvious problem with this is that the way to get by value is much too complicated, and I don't want to have to write out the whole thing every single time I have to reverse lookup.
这样做的明显问题是按值获取的方法太复杂了，我不想每次必须反向查找时都必须写出整个内容。
I just wanted to know: Is there any way to solve this problem without resorting to looping through an object? If not, is there any way to make it easier or cleaner?
我只是想知道：有没有办法解决这个问题而不诉诸循环遍历一个对象？如果没有，有没有办法让它更容易或更干净？
采纳答案by Barmar
Use two objects. One object contains the * -> _asterisk_mapping, the other object contains _asterisk_ -> *.
使用两个对象。一个对象包含* -> _asterisk_映射，另一个对象包含_asterisk_ -> *。
var forwardMap = {'*': '__asterisk__', '%': '__percent__', ...};
var reverseMap = {};
for (var key in forwardMap) {
if (forwardMap.hasOwnProperty(key)) {
reverseMap[forwardMap[key]] = key;
}
}
回答by Edgar Villegas Alvarado
With an extra internal object for reverse mapping. Best if we add a utility class ;) like this:
带有用于反向映射的额外内部对象。最好我们添加一个实用程序类 ;) 像这样：
function TwoWayMap(map) {
this.map = map;
this.reverseMap = {};
for(var key in map) {
var value = map[key];
this.reverseMap[value] = key;
}
}
TwoWayMap.prototype.get = function(key){ return this.map[key]; };
TwoWayMap.prototype.revGet = function(key){ return this.reverseMap[key]; };
Then you instantiate like this:
然后你像这样实例化：
var twoWayMap = new TwoWayMap({
'*' : '__asterisk__',
'%' : '__percent__',
....
});
Then, for using it:
然后，使用它：
twoWayMap.get('*') //Returns '__asterisk__'
twoWayMap.revGet('__asterisk__') //Returns '*'
EDIT: Equivalent with ES6 syntax
编辑：等效于 ES6 语法
class TwoWayMap {
constructor(map) {
this.map = map;
this.reverseMap = {};
for(let key in map) {
const value = map[key];
this.reverseMap[value] = key;
}
}
get(key) { return this.map[key]; }
revGet(key) { return this.reverseMap[key]; }
}
Usage is the same
用法是一样的
Hope this helps. Cheers
希望这可以帮助。干杯
回答by sparrow
回答by harunurhan
I needed something similar, and created https://www.npmjs.com/package/bi-directional-map
我需要类似的东西，并创建了https://www.npmjs.com/package/bi-directional-map
It is implementing a 2-way map using 2 es6 Map, even though it doesn't have a much functionality, it is tested and since it's written typescriptcomes with official typings.
它正在使用 2 es6 Map 实现一个 2-way map，尽管它没有太多功能，但它已经过测试，并且因为它typescript是用官方类型编写的。
回答by AndyL
Some might prefer a more succinct functional style...
有些人可能更喜欢更简洁的功能风格......
const create2WayMap = (seedMap, mapName, reversemapName) => ({
[mapName]: { ...seedMap },
[reversemapName]: Object.keys(seedMap).reduce((map, key) => {
const value = seedMap[key]
return { ...map, [value]: key }
}, {})
})
usage:
用法：
const myIDMap = create2WayMap(
{
1: 'SomeString',
2: 'Another String',
3: 'Another'
},
'idStrings',
'idNumbers'
)
let id = 2
const str = myIDMap.idStrings[id] // yields 'Another String'
id = myIDMap.idNumbers[str] // yields 2
回答by App-Devon
similar to @harunurhan's answer (but much less verbose) I created a small class that takes in a Typescript Map and generates a readonly two-way map:
类似于@harunurhan 的回答（但不那么冗长）我创建了一个小类，它接受一个 Typescript Map 并生成一个只读的双向映射：
export class TwoWayReadonlyMap<T, K> {
map: Map<T, K>;
reverseMap: Map<K, T>;
constructor(map: Map<T, K>) {
this.map = map;
this.reverseMap = new Map<K, T>();
map.forEach((value, key) => {
this.reverseMap.set(value, key);
});
}
get(key: T) {
return this.map.get(key);
}
revGet(key: K) {
return this.reverseMap.get(key);
}
}
