Array 方法 `reduce` 有什么作用? [英] What does the Array method `reduce` do?

问题描述

我发现了一个非常有用的函数reduce，我正在使用它，但我不确定我是否理解正确.谁能帮我理解这个功能?

I found a very useful function reduce, and I'm using it, but I'm not sure if I understand it properly. Can anyone help me to understand this function?

示例:

var arr = [ 1, 2, 3, 4, 5, 6 ];
arr.reduce(function(p,n){
    return p + n;
}, 0);
// Output 21

这是我的理解:reduce 遍历数组的每个元素并返回previous + current value.前任.0 + 1, 1 + 2 等等.在这种情况下这个函数将返回:

This is my understanding: reduce loops through every element of the array and returns previous + current value. Ex. 0 + 1, 1 + 2 etc. In this case this function will return:

[0] - return 1
[1] - return 3
[2] - return 5
[3] - return 7
[4] - return 9
[5] - return 11

接下来呢?为什么它给出结果 21?

What next? Why does it give the result 21?

推荐答案

摘自 此处，arr.reduce() 会将数组减少到回调指定的值.在您的情况下，它基本上会对数组的元素求和.步骤:

Taken from here, arr.reduce() will reduce the array to a value, specified by the callback. In your case, it will basically sum the elements of the array. Steps:

• 在 0,1 上调用函数(0 是作为第二个参数传递给 .reduce() 的初始值.返回 od 0 和 1 的总和，即 1.
• 对前一个结果(即 1 )和下一个数组元素调用函数.这将返回 1 和 2 的总和，即 3
• 重复直到最后一个元素，总和为 21

• Call function on 0,1 ( 0 is the initial value passed to .reduce() as the second argument. Return sum od 0 and 1, which is 1.
• Call function on previous result ( which is 1 ) and next array element. This returns sum of 1 and 2, which is 3
• Repeat until last element, which will sum up to 21

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