How to add to an array in an array JavaScript

Question

I have an array:

["1", "2","3","4","5"]

that I would like to change to:

[["1, 0 ,0 ,0"], ["2, 0, 0, 0"],["3,0,0,0"],["4,0,0,0"],["5,0,0,0"]]

I've tried to achieve this with the following code:

var arr1 = ["1", "2","3","4","5"];
var arr2 = [,"0", "0","0"];
for(var z=0; z<arr1.length; z++)
 {
 arr1[z] = arr1[z].concat(arr2);
 console.log(arr1)
 }
 

However, this doesn't achieve what I want and places commas between each item, which I think is because it is not a string? I've tried using .join too but I couldn't get that to work either. Could someone point me in the right direction for this please? Thanks.

• Daniel A. White: use a new array each time.
• tachko: do you need to combine two arrays for it or are values static?
• Tamane: arr1's values and length is dependent on user input, however, I would always like to add 0, 0, 0 on to each element of arr1, to create an array within an array.
• Rishabh Rawat: let array=[]; for(let i=1;i<=5;i++) array.push([i,0,0,0]); console.log(array)

Answer 1

You first need to convert each element to array and then append the second array to the newly converted array element. The following code snippet would make it clear -

var arr1 = ["1", "2", "3", "4", "5"];
var arr2 = [ "0", "0", "0"];
for (var z = 0; z < arr1.length; z++) {
 // First convert the element into a list
 arr1[z] = [arr1[z]];
 // Then append the second array to it
 arr1[z] = arr1[z].concat(arr2);
 // Another way -
 //arr1[z].push(...arr2);
}
// Final array -
console.log(arr1);

---

Using Map() :

Another way to do it would be using map() as below -

var arr1 = ["1", "2", "3", "4", "5"];
var arr2 = [ "0", "0", "0"];
arr1 = arr1.map(el=>[el,...arr2]);
console.log(arr1);

---

Using ForEach()

You could also do it using forEach() method -

var arr1 = ["1", "2", "3", "4", "5"];
var arr2 = [ "0", "0", "0"];
// this will note mutate original arr1 and store result in res
let res = [];
// ... is the spread operator which will allows iterable objects to be expanded in place
arr1.forEach(el=>res.push([el,...arr2]));
// final result
console.log(res);

---

There's probably numerous other ways as well... These were just few I have listed. You could even do it using naive nested loops method if you don't know anything about map(), forEach(), or concat() / push() methods.

Hope this helps !

Answer 2

Please try the following example

const array = ["1", "2", "3", "4", "5"];
const output = array.map((entry) => [`${entry}, 0, 0, 0`]);
console.log(output);

See

• Array.prototype.map()
• Template literals (Template strings)

Answer 3

if it's set in stone, you can do

let arr = []
var arr1 = ["1", "2","3","4","5"];
var arr2 = ["0", "0","0"];
arr1.forEach(el=>arr.push([el, ...arr2]));
console.log(arr)

Answer 4

Use map to go through each of your element and append the array with zeros, transform it to a string and wrap in an array again which will hold one value

const a = ["1", "2", "3", "4", "5"]
const arr = [0, 0, 0, 0];
const res = a.map(x => [
 [x, ...arr].join()
])
console.log(res)