有没有JavaScript的hashmap库? [英] Is there a hashmap library for JavaScript?
问题描述
toString()
。这意味着: var a = {foo:1};
var b = {bar:2};
var o = {};
o [a] = 100;
o [b]; // 100
JSON.stringify(o); //'{[object Object]:100}'
也就是说,任何普通对象的c $ c> toString()都是 [object Object]
,它们都是地址相同的值。
$ b
我想创建一个散列图,其中具有相同属性和值的对象具有相同的值,但具有不同属性或值的对象具有不同的值。即:
var a = {foo:1};
var b = {bar:2,baz:3};
var c = {baz:3,bar:2};
var hash = new Hash();
hash.set(a,100);
hash.get(b); //未定义
hash.set(b,200);
hash.get(b); // 200
hash.get(c); // 200
我的第一个直觉是使用 JSON.stringify()
将对象转换为字符串,但是:
var hash = {};
var b = {bar:2,baz:3};
var c = {baz:3,bar:2};
hash [JSON.stringify(b)] = 100
hash [JSON.stringify(b)] // 100
hash [JSON.stringify(c)] // undefined
JSON.stringify(b)//'{bar:2,baz:3}'
JSON.stringify(c)//'{baz:3,bar:2} '
也就是说,JSON序列化依赖于顺序。
是否有一个好的库或技术来实现这样的hashmap?
更新:
等价地,是否存在一个很好的散列函数:
$ $ p $ hash({foo:1, bar:2})== hash({bar:2,foo:1})
这是一个快速的概念验证...
我几乎没有测试过它,我确信那里将是无法处理的角落案例。
由于 __ createHash
函数的性能会非常低效需要递归通过任何对象的成员,然后对它们进行排序,以便生成符合您要求的散列。
HashMap = function(){
this。 get = function(key){
var hash = this .__ createHash(key);
返回这个.__ map [hash];
};
this.set = function(key,value){
var hash = this .__ createHash(key);
this .__ map [hash] = value;
};
this .__ createHash = function(key){
switch(typeof key){
case'function':
return'function';
'undefined':
return'undefined';
case'string':
return'''+ key.replace('''''''')+''';
case'对象':
if(!key){
return'null';
}
switch(Object.prototype.toString.apply(key)){
case'[object Array]':
var elements = [];
for(var i = 0; i elements.push( this .__ createHash(key [i]));
}
return'['+ elements.join(',')+']';
case'[object ()
返回'#'+ key.getUTCFullYear()。toString .toString()
+ key.getUTCHours()。toString()
+ key.getUTCMinutes()。toString()
+ key.getUTCSeconds()。toString()+'#';
默认值:
var members = [];
for(var m in key){
members.push(m +'='+ this .__ createHash(key [m]));
}
members.sort();
return'{'+ members.join(',')+'}';
}
默认值:
return key.toString();
}
};
this .__ map = {};
}
In JavaScript, all Objects act a bit like hashmaps. However, the keys to these hashmaps must be strings. If they're not, they're converted with toString()
. That means:
var a = {foo: 1};
var b = {bar: 2};
var o = {};
o[a] = 100;
o[b]; // 100
JSON.stringify(o); // '{"[object Object]":100}'
That is, since the toString()
of any plain Object is [object Object]
, they all address the same value.
I'd like to create a hashmap where Objects with the same properties and values address the same value, but objects with different properties or values address different values. That is:
var a = {foo: 1};
var b = {bar: 2, baz: 3};
var c = {baz: 3, bar: 2};
var hash = new Hash();
hash.set(a, 100);
hash.get(b); // undefined
hash.set(b, 200);
hash.get(b); // 200
hash.get(c); // 200
My first instinct was to use JSON.stringify()
to turn objects into strings, but:
var hash = {};
var b = {bar: 2, baz: 3};
var c = {baz: 3, bar: 2};
hash[JSON.stringify(b)] = 100
hash[JSON.stringify(b)] // 100
hash[JSON.stringify(c)] // undefined
JSON.stringify(b) // '{"bar":2,"baz":3}'
JSON.stringify(c) // '{"baz":3,"bar":2}'
That is, JSON serialization is order-dependent.
Is there a good library or technique to implement a hashmap like this?
Update:
Equivalently, is there a good hashing function such that:
hash({foo: 1, bar: 2}) == hash({bar: 2, foo: 1})
Here's a quick proof-of-concept...
I've hardly tested it at all, and I'm certain that there will be corner-cases that it can't deal with.
Performance will be hideously inefficient because the __createHash
function needs to recurse through the members of any objects and then sort them, in order to generate a "hash" that meets your requirements.
HashMap = function() {
this.get = function(key) {
var hash = this.__createHash(key);
return this.__map[hash];
};
this.set = function(key, value) {
var hash = this.__createHash(key);
this.__map[hash] = value;
};
this.__createHash = function(key) {
switch (typeof key) {
case 'function':
return 'function';
case 'undefined':
return 'undefined';
case 'string':
return '"' + key.replace('"', '""') + '"';
case 'object':
if (!key) {
return 'null';
}
switch (Object.prototype.toString.apply(key)) {
case '[object Array]':
var elements = [];
for (var i = 0; i < key.length; i++) {
elements.push(this.__createHash(key[i]));
}
return '[' + elements.join(',') + ']';
case '[object Date]':
return '#' + key.getUTCFullYear().toString()
+ (key.getUTCMonth() + 1).toString()
+ key.getUTCDate().toString()
+ key.getUTCHours().toString()
+ key.getUTCMinutes().toString()
+ key.getUTCSeconds().toString() + '#';
default:
var members = [];
for (var m in key) {
members.push(m + '=' + this.__createHash(key[m]));
}
members.sort();
return '{' + members.join(',') + '}';
}
default:
return key.toString();
}
};
this.__map = {};
}
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