我需要使用JavaScript来存储一些统计信息,就像在C#中那样:
Dictionary<string, int> statistics;
statistics["Foo"] = 10;
statistics["Goo"] = statistics["Goo"] + 1;
statistics.Add("Zoo", 1);
JavaScript中是否有Hashtable
类似的东西Dictionary<TKey, TValue>
?
如何以这种方式存储值?
我需要使用JavaScript来存储一些统计信息,就像在C#中那样:
Dictionary<string, int> statistics;
statistics["Foo"] = 10;
statistics["Goo"] = statistics["Goo"] + 1;
statistics.Add("Zoo", 1);
JavaScript中是否有Hashtable
类似的东西Dictionary<TKey, TValue>
?
如何以这种方式存储值?
Answers:
关联数组:简单来说,关联数组使用String而不是Integer数字作为索引。
创建一个对象
var dictionary = {};
Javascript允许您使用以下语法向对象添加属性:
Object.yourProperty = value;
相同的替代语法是:
Object["yourProperty"] = value;
如果您还可以使用以下语法创建键值对象映射
var point = { x:3, y:2 };
point["x"] // returns 3
point.y // returns 2
您可以使用for..in循环构造遍历关联数组,如下所示
for(var key in Object.keys(dict)){
var value = dict[key];
/* use key/value for intended purpose */
}
new Array()
被皱眉。该文章最终提到了它的缺点,并提出了建议new Object()
或{}
作为首选的替代方法,但这已经接近尾声了,我担心大多数读者都不会这么想。
var obj1 = {}; var obj2 = {}; var table= {}; table[obj1] = "A"; table[obj2] = "B"; alert(table[obj1]); //displays B
,因为无法区分键obj1和obj2;它们都被转换为字符串,并且变成了类似“对象”之类的东西。完全失败,并且使带有引用和循环引用的类型安全的序列化在JavaScript中完整困难或不起作用。在Flash / AS3中很容易。
Point.prototype.equals = function(obj) { return (obj instanceof Point) && (obj.x === this.x) && (obj.y === this.y); };
for... in
因为字典会在其键上循环播放,所以Object.keys
似乎放错了地方。Object.keys
返回字典的键的数组,for... in
对于一个数组,其循环遍历 其 “键”,对于“数组”,数组是其索引,而不是其值。
var associativeArray = {};
associativeArray["one"] = "First";
associativeArray["two"] = "Second";
associativeArray["three"] = "Third";
如果您来自面向对象的语言,则应查阅本文。
所有现代浏览器都支持javascript Map对象。有两个原因使使用Map比使用Object更好:
- 对象具有原型,因此地图中包含默认键。
- 对象的键是字符串,其中键可以是Map的任何值。
- 当您必须跟踪对象的大小时,可以轻松获取地图的大小。
例:
var myMap = new Map();
var keyObj = {},
keyFunc = function () {},
keyString = "a string";
myMap.set(keyString, "value associated with 'a string'");
myMap.set(keyObj, "value associated with keyObj");
myMap.set(keyFunc, "value associated with keyFunc");
myMap.size; // 3
myMap.get(keyString); // "value associated with 'a string'"
myMap.get(keyObj); // "value associated with keyObj"
myMap.get(keyFunc); // "value associated with keyFunc"
如果要垃圾回收未从其他对象引用的键,请考虑使用WeakMap而不是Map。
Map
当您的键是一个对象但应按值而不是引用进行比较时,这几乎没有用。
除非有特殊原因,否则请使用普通对象。可以使用哈希表样式语法引用Javascript中的对象属性:
var hashtable = {};
hashtable.foo = "bar";
hashtable['bar'] = "foo";
两个foo
和bar
元素,现在则引用如下:
hashtable['foo'];
hashtable['bar'];
// or
hashtable.foo;
hashtable.bar;
当然,这确实意味着您的密钥必须是字符串。如果它们不是字符串,则会在内部将其转换为字符串,因此它可能仍然有效,YMMV。
var hash = {}; hash[1] = "foo"; alert(hash["1"]);
警报“ foo”。
var dict = {}; dict.key1 = "val1"; dict["key2"] = "val2";
dict的key1元素可以同时由dict["key1"]
和引用dict.key1
。
由于JS中的每个对象的行为类似-通常实现为-哈希表,因此我就去做...
var hashSweetHashTable = {};
if (hashSweetHashTable.foo)
应该输入if块if foo
设置。
因此在C#中,代码如下所示:
Dictionary<string,int> dictionary = new Dictionary<string,int>();
dictionary.add("sample1", 1);
dictionary.add("sample2", 2);
要么
var dictionary = new Dictionary<string, int> {
{"sample1", 1},
{"sample2", 2}
};
在JavaScript中
var dictionary = {
"sample1": 1,
"sample2": 2
}
C#字典对象包含有用的方法,例如dictionary.ContainsKey()
在JavaScript中,我们可以使用hasOwnProperty
like
if (dictionary.hasOwnProperty("sample1"))
console.log("sample1 key found and its value is"+ dictionary["sample1"]);
hasOwnProperty
如果您要求键必须是任何对象而不仅仅是字符串,那么可以使用我的jshashtable。
function HashTable() {
this.length = 0;
this.items = new Array();
for (var i = 0; i < arguments.length; i += 2) {
if (typeof (arguments[i + 1]) != 'undefined') {
this.items[arguments[i]] = arguments[i + 1];
this.length++;
}
}
this.removeItem = function (in_key) {
var tmp_previous;
if (typeof (this.items[in_key]) != 'undefined') {
this.length--;
var tmp_previous = this.items[in_key];
delete this.items[in_key];
}
return tmp_previous;
}
this.getItem = function (in_key) {
return this.items[in_key];
}
this.setItem = function (in_key, in_value) {
var tmp_previous;
if (typeof (in_value) != 'undefined') {
if (typeof (this.items[in_key]) == 'undefined') {
this.length++;
} else {
tmp_previous = this.items[in_key];
}
this.items[in_key] = in_value;
}
return tmp_previous;
}
this.hasItem = function (in_key) {
return typeof (this.items[in_key]) != 'undefined';
}
this.clear = function () {
for (var i in this.items) {
delete this.items[i];
}
this.length = 0;
}
}
{}
不是数组:[]
或者new Array()
如果您打算使用字符串键,否则js引擎会出现问题-对于1个变量,它将看到2种类型,这意味着没有优化,或者它将与数组一起运行并实现它必须更改为对象(可能的重新分配)。
我创建此文件是为了解决一些问题,例如对象键映射,枚举(带有forEach()
方法)和清除功能。
function Hashtable() {
this._map = new Map();
this._indexes = new Map();
this._keys = [];
this._values = [];
this.put = function(key, value) {
var newKey = !this.containsKey(key);
this._map.set(key, value);
if (newKey) {
this._indexes.set(key, this.length);
this._keys.push(key);
this._values.push(value);
}
};
this.remove = function(key) {
if (!this.containsKey(key))
return;
this._map.delete(key);
var index = this._indexes.get(key);
this._indexes.delete(key);
this._keys.splice(index, 1);
this._values.splice(index, 1);
};
this.indexOfKey = function(key) {
return this._indexes.get(key);
};
this.indexOfValue = function(value) {
return this._values.indexOf(value) != -1;
};
this.get = function(key) {
return this._map.get(key);
};
this.entryAt = function(index) {
var item = {};
Object.defineProperty(item, "key", {
value: this.keys[index],
writable: false
});
Object.defineProperty(item, "value", {
value: this.values[index],
writable: false
});
return item;
};
this.clear = function() {
var length = this.length;
for (var i = 0; i < length; i++) {
var key = this.keys[i];
this._map.delete(key);
this._indexes.delete(key);
}
this._keys.splice(0, length);
};
this.containsKey = function(key) {
return this._map.has(key);
};
this.containsValue = function(value) {
return this._values.indexOf(value) != -1;
};
this.forEach = function(iterator) {
for (var i = 0; i < this.length; i++)
iterator(this.keys[i], this.values[i], i);
};
Object.defineProperty(this, "length", {
get: function() {
return this._keys.length;
}
});
Object.defineProperty(this, "keys", {
get: function() {
return this._keys;
}
});
Object.defineProperty(this, "values", {
get: function() {
return this._values;
}
});
Object.defineProperty(this, "entries", {
get: function() {
var entries = new Array(this.length);
for (var i = 0; i < entries.length; i++)
entries[i] = this.entryAt(i);
return entries;
}
});
}
Hashtable
get(key)
返回与指定键关联的值。
参数::
key
从中检索值的键。
put(key, value)
将指定的值与指定的键关联。
参数::
key
与值关联的键。
value
:与键关联的值。
remove(key)
删除指定键及其值。
参数::
key
要删除的密钥。
clear()
清除所有哈希表,同时删除键和值。
indexOfKey(key)
根据添加顺序返回指定键的索引。
参数::
key
获取索引的键。
indexOfValue(value)
根据添加顺序返回指定值的索引。
参数::
value
其值获取索引。
注意:
此信息是通过indexOf()
数组的方法检索的,因此它仅将对象与toString()
方法进行比较。
entryAt(index)
返回具有两个属性的对象:键和值,表示指定索引处的条目。
参数::
index
要获取的条目的索引。
containsKey(key)
返回哈希表是否包含指定的键。
参数::
key
要检查的键。
containsValue(value)
返回哈希表是否包含指定值。
参数::
value
要检查的值。
forEach(iterator)
迭代指定中的所有条目iterator
。
参数:
value
::用3个参数的方法key
,value
和index
,其中,index
表示所述条目的索引。
length
(只读)
获取哈希表中条目的计数。
keys
(只读)
获取哈希表中所有键的数组。
values
(只读)
获取哈希表中所有值的数组。
entries
(只读)
获取哈希表中所有条目的数组。它们以与方法相同的形式表示entryAt()
。
https://gist.github.com/alexhawkins/f6329420f40e5cafa0a4
var HashTable = function() {
this._storage = [];
this._count = 0;
this._limit = 8;
}
HashTable.prototype.insert = function(key, value) {
//create an index for our storage location by passing it through our hashing function
var index = this.hashFunc(key, this._limit);
//retrieve the bucket at this particular index in our storage, if one exists
//[[ [k,v], [k,v], [k,v] ] , [ [k,v], [k,v] ] [ [k,v] ] ]
var bucket = this._storage[index]
//does a bucket exist or do we get undefined when trying to retrieve said index?
if (!bucket) {
//create the bucket
var bucket = [];
//insert the bucket into our hashTable
this._storage[index] = bucket;
}
var override = false;
//now iterate through our bucket to see if there are any conflicting
//key value pairs within our bucket. If there are any, override them.
for (var i = 0; i < bucket.length; i++) {
var tuple = bucket[i];
if (tuple[0] === key) {
//overide value stored at this key
tuple[1] = value;
override = true;
}
}
if (!override) {
//create a new tuple in our bucket
//note that this could either be the new empty bucket we created above
//or a bucket with other tupules with keys that are different than
//the key of the tuple we are inserting. These tupules are in the same
//bucket because their keys all equate to the same numeric index when
//passing through our hash function.
bucket.push([key, value]);
this._count++
//now that we've added our new key/val pair to our storage
//let's check to see if we need to resize our storage
if (this._count > this._limit * 0.75) {
this.resize(this._limit * 2);
}
}
return this;
};
HashTable.prototype.remove = function(key) {
var index = this.hashFunc(key, this._limit);
var bucket = this._storage[index];
if (!bucket) {
return null;
}
//iterate over the bucket
for (var i = 0; i < bucket.length; i++) {
var tuple = bucket[i];
//check to see if key is inside bucket
if (tuple[0] === key) {
//if it is, get rid of this tuple
bucket.splice(i, 1);
this._count--;
if (this._count < this._limit * 0.25) {
this._resize(this._limit / 2);
}
return tuple[1];
}
}
};
HashTable.prototype.retrieve = function(key) {
var index = this.hashFunc(key, this._limit);
var bucket = this._storage[index];
if (!bucket) {
return null;
}
for (var i = 0; i < bucket.length; i++) {
var tuple = bucket[i];
if (tuple[0] === key) {
return tuple[1];
}
}
return null;
};
HashTable.prototype.hashFunc = function(str, max) {
var hash = 0;
for (var i = 0; i < str.length; i++) {
var letter = str[i];
hash = (hash << 5) + letter.charCodeAt(0);
hash = (hash & hash) % max;
}
return hash;
};
HashTable.prototype.resize = function(newLimit) {
var oldStorage = this._storage;
this._limit = newLimit;
this._count = 0;
this._storage = [];
oldStorage.forEach(function(bucket) {
if (!bucket) {
return;
}
for (var i = 0; i < bucket.length; i++) {
var tuple = bucket[i];
this.insert(tuple[0], tuple[1]);
}
}.bind(this));
};
HashTable.prototype.retrieveAll = function() {
console.log(this._storage);
//console.log(this._limit);
};
/******************************TESTS*******************************/
var hashT = new HashTable();
hashT.insert('Alex Hawkins', '510-599-1930');
//hashT.retrieve();
//[ , , , [ [ 'Alex Hawkins', '510-599-1930' ] ] ]
hashT.insert('Boo Radley', '520-589-1970');
//hashT.retrieve();
//[ , [ [ 'Boo Radley', '520-589-1970' ] ], , [ [ 'Alex Hawkins', '510-599-1930' ] ] ]
hashT.insert('Vance Carter', '120-589-1970').insert('Rick Mires', '520-589-1970').insert('Tom Bradey', '520-589-1970').insert('Biff Tanin', '520-589-1970');
//hashT.retrieveAll();
/*
[ ,
[ [ 'Boo Radley', '520-589-1970' ],
[ 'Tom Bradey', '520-589-1970' ] ],
,
[ [ 'Alex Hawkins', '510-599-1930' ],
[ 'Rick Mires', '520-589-1970' ] ],
,
,
[ [ 'Biff Tanin', '520-589-1970' ] ] ]
*/
//overide example (Phone Number Change)
//
hashT.insert('Rick Mires', '650-589-1970').insert('Tom Bradey', '818-589-1970').insert('Biff Tanin', '987-589-1970');
//hashT.retrieveAll();
/*
[ ,
[ [ 'Boo Radley', '520-589-1970' ],
[ 'Tom Bradey', '818-589-1970' ] ],
,
[ [ 'Alex Hawkins', '510-599-1930' ],
[ 'Rick Mires', '650-589-1970' ] ],
,
,
[ [ 'Biff Tanin', '987-589-1970' ] ] ]
*/
hashT.remove('Rick Mires');
hashT.remove('Tom Bradey');
//hashT.retrieveAll();
/*
[ ,
[ [ 'Boo Radley', '520-589-1970' ] ],
,
[ [ 'Alex Hawkins', '510-599-1930' ] ],
,
,
[ [ 'Biff Tanin', '987-589-1970' ] ] ]
*/
hashT.insert('Dick Mires', '650-589-1970').insert('Lam James', '818-589-1970').insert('Ricky Ticky Tavi', '987-589-1970');
hashT.retrieveAll();
/* NOTICE HOW HASH TABLE HAS NOW DOUBLED IN SIZE UPON REACHING 75% CAPACITY ie 6/8. It is now size 16.
[,
,
[ [ 'Vance Carter', '120-589-1970' ] ],
[ [ 'Alex Hawkins', '510-599-1930' ],
[ 'Dick Mires', '650-589-1970' ],
[ 'Lam James', '818-589-1970' ] ],
,
,
,
,
,
[ [ 'Boo Radley', '520-589-1970' ],
[ 'Ricky Ticky Tavi', '987-589-1970' ] ],
,
,
,
,
[ [ 'Biff Tanin', '987-589-1970' ] ] ]
*/
console.log(hashT.retrieve('Lam James')); //818-589-1970
console.log(hashT.retrieve('Dick Mires')); //650-589-1970
console.log(hashT.retrieve('Ricky Ticky Tavi')); //987-589-1970
console.log(hashT.retrieve('Alex Hawkins')); //510-599-1930
console.log(hashT.retrieve('Lebron James')); //null
您可以使用以下方法创建一个:
var dictionary = { Name:"Some Programmer", Age:24, Job:"Writing Programs" };
//Iterate Over using keys
for (var key in dictionary) {
console.log("Key: " + key + " , " + "Value: "+ dictionary[key]);
}
//access a key using object notation:
console.log("Her Name is: " + dictionary.Name)