Javascript 创建一个重复多次相同元素的数组
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Create an array with same element repeated multiple times
提问by Curious2learn
In Python, where [2]is a list, the following code gives this output:
在 Python 中， where[2]是一个列表，下面的代码给出了这个输出：
[2] * 5 # Outputs: [2,2,2,2,2]
Does there exist an easy way to do this with an array in JavaScript?
是否有一种简单的方法可以用 JavaScript 中的数组来做到这一点？
I wrote the following function to do it, but is there something shorter or better?
我编写了以下函数来做到这一点，但有更短或更好的吗？
var repeatelem = function(elem, n){
// returns an array with element elem repeated n times.
var arr = [];
for (var i = 0; i <= n; i++) {
arr = arr.concat(elem);
};
return arr;
};
采纳答案by Guffa
You can do it like this:
你可以这样做：
function fillArray(value, len) {
if (len == 0) return [];
var a = [value];
while (a.length * 2 <= len) a = a.concat(a);
if (a.length < len) a = a.concat(a.slice(0, len - a.length));
return a;
}
It doubles the array in each iteration, so it can create a really large array with few iterations.
它在每次迭代中将数组加倍，因此它可以通过很少的迭代创建一个非常大的数组。
Note: You can also improve your function a lot by using pushinstead of concat, as concatwill create a new array each iteration. Like this (shown just as an example of how you can work with arrays):
注意：您还可以通过使用push代替 来改进您的函数concat，因为concat每次迭代都会创建一个新数组。像这样（仅作为如何使用数组的示例显示）：
function fillArray(value, len) {
var arr = [];
for (var i = 0; i < len; i++) {
arr.push(value);
}
return arr;
}
回答by Niko Ruotsalainen
回答by Janus Troelsen
>>> Array.apply(null, Array(10)).map(function(){return 5})
[5, 5, 5, 5, 5, 5, 5, 5, 5, 5]
>>> //Or in ES6
>>> [...Array(10)].map((_, i) => 5)
[5, 5, 5, 5, 5, 5, 5, 5, 5, 5]
回答by Vivek
you can try:
你可以试试：
Array(6).join('a').split(''); // returns ['a','a','a','a','a'] (5 times)
Update (01/06/2018):
更新（01/06/2018）：
Now you can have a set of characters repeating.
现在你可以有一组重复的字符。
new Array(5).fill('a'); // give the same result as above;
// or
Array.from({ length: 5 }).fill('a')
Note: Check more about fill(...)and from(...)for compatibility and browser support.
注意：查看更多关于fill(...)和from(...)的兼容性和浏览器支持。
Update (05/11/2019):
更新（05/11/2019）：
Another way, without using fillor from, that works for string of any length:
另一种不使用fillor 的方法from适用于任何长度的字符串：
Array.apply(null, Array(3)).map(_ => 'abc') // ['abc', 'abc', 'abc']
Same as above answer. Adding for sake of completeness.
与上述答案相同。为了完整性而添加。
回答by Thomson
Array.from({length:5}, i => 1) // [1, 1, 1, 1, 1]
Array.from({length:5}, i => 1) // [1, 1, 1, 1, 1]
or create array with increasing value
或创建具有递增值的数组
Array.from({length:5}, (e, i)=>i) // [0, 1, 2, 3, 4]
Array.from({length:5}, (e, i)=>i) // [0, 1, 2, 3, 4]
回答by Droogans
回答by brook hong
[c] * ncan be written as:
[c] * n可以写成：
Array(n+1).join(1).split('').map(function(){return c;})
so for [2] * 5
因此对于 [2] * 5
Array(6).join(1).split('').map(function(){return 2;})
回答by Shmiddty
You can also extend the functionality of Array like so:
您还可以像这样扩展 Array 的功能：
Array.prototype.fill = function(val){
for (var i = 0; i < this.length; i++){
this[i] = val;
}
return this;
};
// used like:
var arry = new Array(5)?.fill(2);
// or
var arry = new Array(5);
arry.fill(2);
?console.log(arry);? //[2, 2, 2, 2, 2]
I should note that extending the functionality of built-in objects can cause problems if you are working with 3rd-party libraries. Always weigh this into your decisions.
我应该注意，如果您正在使用 3rd-party 库，扩展内置对象的功能可能会导致问题。始终在您的决定中权衡这一点。
回答by Henrik Christensen
In case you need to repeat an arrayseveral times:
如果您需要多次重复数组：
var arrayA = ['a','b','c'];
var repeats = 3;
var arrayB = Array.apply(null, {length: repeats * arrayA.length})
.map(function(e,i){return arrayA[i % arrayA.length]});
// result: arrayB = ['a','b','c','a','b','c','a','b','c']
inspired by this answer
受到这个答案的启发
回答by noobninja
In the Node.js REPL:
在 Node.js REPL 中：
> Array.from({length:5}).map(x => 2)
[ 2, 2, 2, 2, 2 ]
