如何比较 JavaScript 中的数组? [英] How to compare arrays in JavaScript?
问题描述
我想比较两个数组......理想情况下，有效地.没什么特别的，如果它们相同，就 true ，否则 false .毫不奇怪，比较运算符似乎不起作用.
I'd like to compare two arrays... ideally, efficiently. Nothing fancy, just true if they are identical, and false if not. Not surprisingly, the comparison operator doesn't seem to work.
var a1 = [1,2,3];
var a2 = [1,2,3];
console.log(a1==a2); // Returns false
console.log(JSON.stringify(a1)==JSON.stringify(a2)); // Returns true
JSON 编码每个数组都可以，但是有没有更快或更好"的方法来简单地比较数组而不必遍历每个值?
JSON encoding each array does, but is there a faster or "better" way to simply compare arrays without having to iterate through each value?
推荐答案
要比较数组，请遍历它们并比较每个值:
To compare arrays, loop through them and compare every value:
// Warn if overriding existing method
if(Array.prototype.equals)
console.warn("Overriding existing Array.prototype.equals. Possible causes: New API defines the method, there's a framework conflict or you've got double inclusions in your code.");
// attach the .equals method to Array's prototype to call it on any array
Array.prototype.equals = function (array) {
// if the other array is a falsy value, return
if (!array)
return false;
// compare lengths - can save a lot of time
if (this.length != array.length)
return false;
for (var i = 0, l=this.length; i < l; i++) {
// Check if we have nested arrays
if (this[i] instanceof Array && array[i] instanceof Array) {
// recurse into the nested arrays
if (!this[i].equals(array[i]))
return false;
}
else if (this[i] != array[i]) {
// Warning - two different object instances will never be equal: {x:20} != {x:20}
return false;
}
}
return true;
}
// Hide method from for-in loops
Object.defineProperty(Array.prototype, "equals", {enumerable: false});
用法:
[1, 2, [3, 4]].equals([1, 2, [3, 2]]) === false;
[1, "2,3"].equals([1, 2, 3]) === false;
[1, 2, [3, 4]].equals([1, 2, [3, 4]]) === true;
[1, 2, 1, 2].equals([1, 2, 1, 2]) === true;
您可能会说但是比较字符串要快得多 - 没有循环......"；好吧，那么您应该注意存在 ARE 循环.第一个递归循环将 Array 转换为字符串，第二个递归循环比较两个字符串.所以这个方法比使用字符串要快.
You may say "But it is much faster to compare strings - no loops..." well, then you should note there ARE loops. First recursive loop that converts Array to string and second, that compares two strings. So this method is faster than use of string.
我相信大量的数据应该总是存储在数组中，而不是存储在对象中.但是，如果您使用对象，它们也可以部分比较.
方法如下:
我在上面说过，两个对象实例永远不会相等，即使它们此刻包含相同的数据:
I've stated above, that two object instances will never be equal, even if they contain same data at the moment:
({a:1, foo:"bar", numberOfTheBeast: 666}) == ({a:1, foo:"bar", numberOfTheBeast: 666}) //false
这是有原因的，因为可能存在例如对象内的私有变量.
This has a reason, since there may be, for example private variables within objects.
但是，如果你只是使用对象结构来包含数据，比较仍然是可能的:
However, if you just use object structure to contain data, comparing is still possible:
Object.prototype.equals = function(object2) {
//For the first loop, we only check for types
for (propName in this) {
//Check for inherited methods and properties - like .equals itself
//https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/hasOwnProperty
//Return false if the return value is different
if (this.hasOwnProperty(propName) != object2.hasOwnProperty(propName)) {
return false;
}
//Check instance type
else if (typeof this[propName] != typeof object2[propName]) {
//Different types => not equal
return false;
}
}
//Now a deeper check using other objects property names
for(propName in object2) {
//We must check instances anyway, there may be a property that only exists in object2
//I wonder, if remembering the checked values from the first loop would be faster or not
if (this.hasOwnProperty(propName) != object2.hasOwnProperty(propName)) {
return false;
}
else if (typeof this[propName] != typeof object2[propName]) {
return false;
}
//If the property is inherited, do not check any more (it must be equa if both objects inherit it)
if(!this.hasOwnProperty(propName))
continue;
//Now the detail check and recursion
//This returns the script back to the array comparing
/**REQUIRES Array.equals**/
if (this[propName] instanceof Array && object2[propName] instanceof Array) {
// recurse into the nested arrays
if (!this[propName].equals(object2[propName]))
return false;
}
else if (this[propName] instanceof Object && object2[propName] instanceof Object) {
// recurse into another objects
//console.log("Recursing to compare ", this[propName],"with",object2[propName], " both named \""+propName+"\"");
if (!this[propName].equals(object2[propName]))
return false;
}
//Normal value comparison for strings and numbers
else if(this[propName] != object2[propName]) {
return false;
}
}
//If everything passed, let's say YES
return true;
}
但是，请记住，这是用于比较 JSON 之类的数据，而不是类实例和其他东西.如果你想比较更复杂的对象，看看这个答案，它的超长函数.
要使用 Array.equals 进行此操作，您必须稍微编辑原始函数:
However, remember that this one is to serve in comparing JSON like data, not class instances and other stuff. If you want to compare more complicated objects, look at this answer and it's super long function.
To make this work with Array.equals you must edit the original function a little bit:
...
// Check if we have nested arrays
if (this[i] instanceof Array && array[i] instanceof Array) {
// recurse into the nested arrays
if (!this[i].equals(array[i]))
return false;
}
/**REQUIRES OBJECT COMPARE**/
else if (this[i] instanceof Object && array[i] instanceof Object) {
// recurse into another objects
//console.log("Recursing to compare ", this[propName],"with",object2[propName], " both named \""+propName+"\"");
if (!this[i].equals(array[i]))
return false;
}
else if (this[i] != array[i]) {
...
我为这两个功能做了一个小测试工具.
I made a little test tool for both of the functions.
Samy Bencherif 准备了有用在嵌套数组中搜索特定对象的情况下的函数，可在此处获得:https://jsfiddle.net/SamyBencherif/8352y6yw/
Samy Bencherif has prepared useful functions for the case you're searching for a specific object in nested arrays, which are available here: https://jsfiddle.net/SamyBencherif/8352y6yw/
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