我想比较两个数组......理想情况下,有效。没什么花哨的,如果它们相同,则为 true
,如果不同,则为 false
。毫不奇怪,比较运算符似乎不起作用。
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
每个数组都可以进行 JSON 编码,但是有没有更快或“更好”的方法来简单地比较数组,而不必迭代每个值?
最佳答案
要比较数组,请循环遍历它们并比较每个值:
比较数组:
// 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;
// if the argument is the same array, we can be sure the contents are same as well
if(array === this)
return true;
// 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...”那么您应该注意到存在循环。第一个递归循环将数组转换为字符串,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更快。
我认为大量数据应该始终存储在数组中,而不是对象中。但是,如果您使用对象,它们也可以进行部分比较。
方法如下:
比较对象:
我在上面已经说过,两个对象实例永远不会相等,即使它们当前包含相同的数据:
({a:1, foo:"bar", numberOfTheBeast: 666}) == ({a:1, foo:"bar", numberOfTheBeast: 666}) //false
这是有原因的,因为可能有,例如private variables within objects.
但是,如果只是使用对象结构来包含数据,仍然可以进行比较:
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内容。如果您想比较更复杂的对象,请查看 this answer and it's super long function 。
要使此功能与 Array.equals 一起使用,您必须稍微编辑原始函数:
...
// 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]) {
...
我做了一个 little test tool for both of the functions 。
奖励:带有 indexOf
和 contains
的嵌套数组
Samy Bencherif has prepared 对于在嵌套数组中搜索特定对象的情况有用的函数,可在此处找到:https://jsfiddle.net/SamyBencherif/8352y6yw/
关于javascript - 如何在 JavaScript 中比较数组?,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/31004797/