问题

我想要比较两个数组...理想情况下,高效.没有什么奇怪,只要 true 如果他们是相同的,和 false 如果没有.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

对每个数组进行JSON编码,但是有没有更快或更好的方法来简单地比较数组,而不必遍历每个值?



解决方法

我真的不敢相信这么多人想把数组作为字符串进行比较.所以,虽然这是老问题,我将添加方式比较数组 - 循环通过它们并比较每个值:

The right way:

// 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});

Usage:

[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;

您可以说"但是它比比较字符串更快 - 没有循环... ",那么你应该注意到有ARE循环.第一个递归循环将数组转换为字符串,第二个循环将比较两个字符串.因此,此方法比使用字符串更快.

我相信大量的数据应该总是存储在数组中,而不是对象中.但是,如果您使用对象,它们也可以部分比较 操作方法如下:

Comparing objects:

我上面已经说过,两个对象实例永远不会相等,即使它们现在包含相同的数据:

({a:1, foo:"bar", numberOfTheBeast: 666}) == ({a:1, foo:"bar", numberOfTheBeast: 666})  //false

这有一个原因,因为例如可能有对象中的私有变量.

但是,如果只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,这一个是用于比较JSON像数据,而不是类实例和其他东西.如果您想比较复杂的对象,请查看此答案,它的超长函数. 要使这个工作与 Array.equals 您必须编辑原始的函数一点:

...
    // 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]) {
...

我为这两个功能制作了小测试工具.

Bonus: Nested arrays with indexOf and contains

Samy Bencherif已准备好有用的函数用于在嵌套数组中搜索特定对象的情况,可在此处访问: https:// jsfiddle .net / SamyBencherif / 8352y6yw /




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