javascript 如何复制js数组中的元素？
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How to duplicate elements in a js array?
提问by Jan Rüegg
Whats the easiest way (with "native" javascript) to duplicate every element in a javascript array?
复制 javascript 数组中每个元素的最简单方法是什么（使用“本机”javascript）？
The order matters.
顺序很重要。
For example:
例如：
a = [2, 3, 1, 4]
// do something with a
a
// a is now [2, 2, 3, 3, 1, 1, 4, 4]
回答by axelduch
回答by morels
Basically:
基本上：
a = [2, 3, 1, 4];
b=[];
for(var i = 0; i< a.length;++i){
b.push(a[i]);
b.push(a[i]);
}
a=b;
回答by tymeJV
I suppose you could do:
我想你可以这样做：
var duplicated = a.map(function(item) {
return [item, item];
}).reduce(function(a, b) { return a.concat(b) });
//duplicated: [2, 2, 3, 3, 1, 1, 4, 4]
回答by Bamieh
I came across this issue in my application, so I created this function:
我在我的应用程序中遇到了这个问题，所以我创建了这个函数：
function duplicateElements(array, times) {
return array.reduce((res, current) => {
return res.concat(Array(times).fill(current));
}, []);
}
To use it, simple pass the array, and the number of times you want the elements to be duplicated:
要使用它，只需传递数组，以及您希望元素被复制的次数：
duplicateElements([2, 3, 1, 4], 2);
// returns: [2, 2, 3, 3, 1, 1, 4, 4]
回答by Zeyad Etman
Basically you can use flatMapin ES19
基本上你可以flatMap在 ES19 中使用
a = [1, 2, 3, 4];
a.flatMap(i => [i,i]); // [1, 1, 2, 2, 3, 3, 4, 4]
Also you can customize the repetitions number like this:
您也可以像这样自定义重复次数：
a = [1, 2, 3, 4];
const dublicateItems = (arr, numberOfRepetitions) =>
arr.flatMap(i => Array.from({ length: numberOfRepetitions }).fill(i));
dublicateItems(a, 3);
回答by fix-me
how 'bout that?
怎么样？
for (i=a.length-1;i>=0;i--)a.splice(i,0,a[i]);
iterating backwards is undervalued, in this case it keeps the index intact ;)
向后迭代被低估了，在这种情况下它保持索引完整；)
回答by Nina Scholz
Just splice a little bit.
只需拼接一点。
var a = [2, 3, 1, 4],
i = a.length;
while (i--) {
a.splice(i, 0, a[i]);
}
document.write('<pre>' + JSON.stringify(a, 0, 4) + '</pre>');回答by tallgirltaadaa
These functions may help see .sort(), .concat()
这些函数可能有助于查看 .sort(), .concat()
function duplicate(arr) {
return arr.concat(arr).sort()
}
console.log(duplicate([1,2,3,4,5]))
回答by yckart
0/2 = 0 = 0 |0 = 0
1/2 = 0.5 = 0.5|0 = 0
2/2 = 1 = 1 |0 = 1
3/2 = 1.5 = 1.5|0 = 1
4/2 = 2 = 2 |0 = 2
5/2 = 2.5 = 2.5|0 = 2
6/2 = 3 = 3 |0 = 3
7/2 = 3.5 = 3.5|0 = 3
Treat |0as Math.floor
治疗|0的Math.floor
In code this could look like this:
在代码中，这可能如下所示：
for (let i = 0; i < a.length * 2; i++) {
a[i] = a[i / 2 |?0]
}
Because immutability is preferable, one could do something like this:
因为不变性是可取的，所以可以做这样的事情：
function repeatItems(a, n) {
const b = new Array(a.length * n)
for (let i = 0; i < b.length; i++) {
b[i] = a[i / n | 0]
}
return b
}
Unreadable ES6 spaghetti code:
不可读的 ES6 意大利面代码：
const repeatItems = (a, n) => Array.from(Array(a.length * n), (_, i) => a[i / n | 0])
回答by radzak
ES6 way of life (based on axelduch'sanswer)
ES6 的生活方式（基于axelduch 的回答）
const arr = [2, 3, 1, 4].reduce((res, current) => [...res, current, current], []);
console.log(arr);