"But I always double the numbers. so [1,1,2,2,3,3 .......] how can you do that? I am looking forward to the answer. " Continuous with a number, the for loop is good. But how do I do it with double numbers?
2 Answers
To get an array to N, use:
let N = 10;
Array.from(Array(N).keys())
To double each value in any array:
[...yourArray.map(n => [n, n])].flat()
So, your solution:
let n = 10;
const a = [...Array.from(Array(n).keys()).map(k => [k, k])].flat()
console.log(a)To have it starting from 0, not 1, alter the mapping accordingly:
let n = 10;
const a = [
...Array.from(Array(n).keys())
.map(k => [k + 1, k + 1])
].flat()
console.log(a)Arguably, the cleanest solution:
function doubleArrayTo(n) {
const a = [];
for (i = 1; i <= n; i++) {
a.push(i, i);
}
return a;
}
console.log(doubleArrayTo(10))Out of curiosity, I tested their performance. Unsurprisingly, the for loop wins hands down over the spread syntax:
function doubleFor(n) {
const a = [];
for (i = 1; i <= n; i++) {
a.push(i, i);
}
return a;
}
function doubleSpread(n) {
return [
...Array.from(Array(n).keys())
.map(k => [k + 1, k + 1])
].flat()
}
function run_test(fn, value) {
const t0 = performance.now();
fn(value);
return performance.now() - t0;
}
[1e4, 1e5, 1e6, 1e7].map(value => {
console.log(
`(${value}): for => ${
run_test(doubleFor, value)
} | spread => ${
run_test(doubleSpread, value)
}`);
});
Comments
follow this code
var array = [];
for(int i = 0;i <= 10;i++) {
array.push(i);
array.push(i);//again
}
var array = [];
for (let i = 0; i <= 10; i++) {
array.push(i,i);
}
console.log(array);Edit
You can use multi input for array.push(i,i,i,....)
1 Comment
tao
Why not
array.push(i,i)?
arr.push(i);toarr.push(i);arr.push(i);?arr.push(i, i)?