Javascript 生成空二维数组的最佳方法
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原文地址: http://stackoverflow.com/questions/6495187/
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best way to generate empty 2D array
提问by vsync
is there a shorter, better way to generate 'n' length 2D array?
有没有更短、更好的方法来生成“n”长度的二维数组？
var a = (function(){ var i=9, arr=[]; while(i--) arr.push([]); return arr })();
a // [ [],[],[],[],[],[],[],[],[] ]
** old-school short-way**:
** 老式短途**：
var a = (function(a){ while(a.push([]) < 9); return a})([]);
UPDATE - Using ES2015
更新 - 使用 ES2015
Array(5).fill().map(a=>[]); // will create 5 Arrays in an Array
// or
Array.from({length:5}, a=>[])
Emptying 2D array(saves memory rather)
清空二维数组（更节省内存）
function make2dArray(len){
var a = [];
while(a.push([]) < len);
return a;
}
function empty2dArray(arr){
for( var i = arr.length; i--; )
arr[i].length = 0;
}
// lets make a 2D array of 3 items
var a = make2dArray(3);
// lets populate it a bit
a[2].push('demo');
console.log(a); // [[],[],["demo"]]
// clear the array
empty2dArray(a);
console.log(a); // [[],[],[]]
回答by Felix Kling
Another way:
其它的办法：
for(var a = [];a.length < 10; a.push([])); // semicolon is mandatory here
Yet another way:
还有一种方式：
var a = []; while(a.push([]) < 10);
This works because .push()[docs](specification) returns the new length of the array.
这是有效的，因为.push()[docs]（规范）返回数组的新长度。
That said, this is the wrong way of "reducing code". Create a dedicated function with a meaningful name and use this one. Your code will be much more understandable:
也就是说，这是“减少代码”的错误方式。创建一个具有有意义名称的专用函数并使用这个函数。你的代码会更容易理解：
function get2DArray(size) {
size = size > 0 ? size : 0;
var arr = [];
while(size--) {
arr.push([]);
}
return arr;
}
var a = get2DArray(9);
Code is read much more often than written.
代码的阅读频率远高于编写代码。
回答by Xlee
Just discovered another ES6way with one line expression:
刚刚用一行表达式发现了另一种ES6方式：
Array.from({length: N}, () => [])
Array.from(arrayLike[, mapFn[, thisArg]])
Array.from(arrayLike[, mapFn[, thisArg]])
More detail about its implementation/polyfill ? MDN Array.from()
有关其实现/polyfill 的更多详细信息？MDN Array.from()
Yet another neat solution with help of array spread syntax:
另一个巧妙的解决方案，帮助array spread syntax：
[...Array(N)].map(() => [])
回答by sugavaneshb
Array(cardinality).fill(0).map(function(item) {return [];});
where cardinality is the number of items you are looking at. In this case it would be 9. This was suggested by one of my colleagues actually. This is neat, I think :) This is valid from ECMA V6. Documentation: Array::fill
其中基数是您正在查看的项目数。在这种情况下，它将是 9。这实际上是我的一位同事建议的。这很好，我认为 :) 这从 ECMA V6 开始有效。文档：数组::填充
回答by user1542
for(var i=9,a=[];i>=0;i--){ a.push([]) }
回答by user1542
In ES6:
在 ES6 中：
(m, n, initialElementValue) => Array(m).fill(Array(n).fill(initialElementValue))
回答by Sergey Semushin
var x = 3, y = 5, arr = Array(y).fill();
arr = arr.map(function(){return Array(x).fill(' ')});
console.log(arr);回答by Zum Dummi
best way to generate 2D array in js by ES6 by Array.from
通过 ES6 在 js 中生成二维数组的最佳方法 Array.from
function twodimension(input) {
let index = 0,
sqrt = Math.sqrt(input.length);
return Array.from({
length: sqrt
}, (nothing, i) => Array.from({
length: sqrt
}, (nothingTwo, j) => input[index++]))
}
console.log(twodimension('abcdefghijklmnopqrstupwxy'))
console.log(twodimension([1,2,3,4,5,6,7,8,9]))function input(length, fill) {
let getNums = length * length;
let fillNums = 1
if (fill == 'minus') {
return Array.from({
length: length
}, (nothing, i) => Array.from({
length: length
}, (nothingTwo, j) => getNums--))
} else if (fill == 'plus') {
return Array.from({
length: length
}, (nothing, i) => Array.from({
length: length
}, (nothingTwo, j) => fillNums++))
}
// you can dping snake ladders also with Array.from
if (fill === 'snakes') {
return Array.from({
length: length
}, (_, one) =>
Array.from({
length: length
}, (_, two) => getNums--)
).map((el, i) =>
i % 2 == 1 && length % 2 == 0 ? el.reverse() :
i % 2 == 0 && length % 2 == 1 ? el.reverse() : el
);
}
}
console.log(input(8, 'minus'))
console.log(input(10, 'plus'))
console.log(input(5, 'snakes'))you do anything with Array.from, it is easy to use and fast, this is the new method in ES6 syntax
你可以用Array.from做任何事情，它易于使用且速度快，这是ES6语法中的新方法
回答by Nathan Romano
var a = []; for(var i=0;i<10;i++) { a[i] = []; }
回答by malko
shorter way can be :
更短的方法可以是：
for(var i=9,a=[];i>=0;i--){ a.push([]) }
回答by Naftali aka Neal
var a = [];
var max_length = 10;
for(var i = 0; i < max_length; ++i){
a[i] = [];
}
