Javascript:推入一个空的 3d 数组 [英] Javascript: Pushing in an Empty 3d Array

问题描述

我创建了一个空的 3x3x1 3D 数组

<预><代码>[[[],[],[]],[[],[],[]],[[],[],[]]]

现在，位置arr[1][1]的元素是[]，所以，如果我执行arr[1][1].push(1) 它应该在 arr[1][1]

位置插入 1

在JS中有2种方法可以创建一个空的3x3x1数组，代码如下，

var arr1 = [...new Array(3)].map(e => [...new Array(3)].fill([]));var arr2 = [[[],[],[]],[[],[],[]],[[],[],[]]];arr1[1][1].push(1);arr2[1][1].push(1);控制台日志(arr1)控制台日志(arr2)

即.通过快捷方式和另一个手动，arr1和arr2应该是一样的，所以应该是输出，但是输出如下，

[[[], [], []], [[1], [1], [1]], [[], [], []]][[[], [], []], [[], [1], []], [[], [], []]]

为什么第一个数组给出这样的输出?两者不一样吗?

我希望输出是第二种形式，如果这是创建空的 3x3x1 数组的错误方法，请提出一种方法，以便提供预期的输出.

解决方案

再使用一张嵌套映射.我认为 fill 调用将用 same 数组填充第一个 map 在每个第二维中，而不是唯一的，这意味着第二个维度维度都引用同一个数组.

来自 fill 的文档 甚至要注意 value 将完全相同:

<块引用>

用于填充数组的值.(注意数组中的所有元素都将是这个确切的值.)

还有(数组是一个对象):

<块引用>

如果第一个参数是一个对象，则数组中的每个槽都将引用该对象.

const arr1 = [...new Array(3)].map(e => [...new Array(3)].充满([]));const arr2 = [[[],[],[]],[[],[],[]],[[],[],[]]];const arr3 = [...new Array(3)].map(() => [...new Array(3)].map(() => []));arr1[1][1].push(1);arr2[1][1].push(1);arr3[1][1].push(1);console.log(JSON.stringify(arr1));//[[[],[],[]],[[1],[1],[1]],[[],[],[]]]console.log(JSON.stringify(arr2));//[[[],[],[]],[[],[1],[]],[[],[],[]]]console.log(JSON.stringify(arr3));//[[[],[],[]],[[],[1],[]],[[],[],[]]]

换句话说:

const expandArr1 = [...new Array(3)].map(() => {/** 来自 MDN 填写文档:* 用于填充数组的值.(注意数组中的所有元素都将是这个确切的值.)*/返回 [...new Array(3)].fill([]);//每个元素都会得到这个确切的值(参考)});//它们是相同的引用:console.log(expandedArr1[1][1] === ExpandedArr1[1][2]);

I create an empty 3x3x1 3D array

[
  [[],[],[]],
  [[],[],[]],
  [[],[],[]]
]

Now, The element at position arr[1][1] is [], So, If I execute arr[1][1].push(1) it should insert 1 on position arr[1][1]

There are 2 methods for creating an empty 3x3x1 array in JS, Here is the code,

var arr1 = [...new Array(3)].map(e => [...new Array(3)].fill([]));
var arr2 = [[[],[],[]],[[],[],[]],[[],[],[]]];
arr1[1][1].push(1);
arr2[1][1].push(1);
console.log(arr1)
console.log(arr2)

ie. Through shortcut and another manually, both arr1 and arr2 should be identical, so should be the output, But the output is as follows,

[[[], [], []], [[1], [1], [1]], [[], [], []]]

[[[], [], []], [[], [1], []], [[], [], []]]

Why is it that first array gives such output? Aren't both identical?

I want the output to be of the 2nd form, If this is a wrong way to create an empty 3x3x1 array, please suggest a method such that it gives expected output.

解决方案

Use one more nested map. I think that fill call will fill the first map with the same array in each of the 2nd dimension instead of a unique one which means the 2nd dimension all reference the same array.

The docs from fill even note that the value will be the exact same:

Value to fill the array with. (Note all elements in the array will be this exact value.)

Also (array is an object):

If the first parameter is an object, each slot in the array will reference that object.

const arr1 = [...new Array(3)].map(e => [...new Array(3)].fill([]));
const arr2 = [[[],[],[]],[[],[],[]],[[],[],[]]];
const arr3 = [...new Array(3)].map(() => [...new Array(3)].map(() => []));

arr1[1][1].push(1);
arr2[1][1].push(1);
arr3[1][1].push(1);

console.log(JSON.stringify(arr1)); // [[[],[],[]],[[1],[1],[1]],[[],[],[]]]
console.log(JSON.stringify(arr2)); // [[[],[],[]],[[],[1],[]],[[],[],[]]]
console.log(JSON.stringify(arr3)); // [[[],[],[]],[[],[1],[]],[[],[],[]]]

In other words:

const expandedArr1 = [...new Array(3)].map(() => {
  /*
   * From MDN fill documentation:
   * Value to fill the array with. (Note all elements in the array will be this exact value.)
   */
  return [...new Array(3)].fill([]); // Every element will get this exact value (reference)
});

// They are the same reference:
console.log(expandedArr1[1][1] === expandedArr1[1][2]);

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