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.

do you need to combine two arrays for it or are values static? — tachko
– tachko, Commented Jun 29, 2020 at 18:59
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. — Tamane
– Tamane, Commented Jun 29, 2020 at 19:02
let array=[]; for(let i=1;i<=5;i++) array.push([i,0,0,0]); console.log(array); — Rishabh Rawat
– Rishabh Rawat, Commented Jun 29, 2020 at 19:07

Abhishek Bhagate · Accepted Answer · 2020-06-29 19:21:22Z

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 !

Mario · Accepted Answer · 2020-06-29 19:05:31Z

1

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

answered Jun 29, 2020 at 19:05

Mario

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Comments

tachko · Accepted Answer · 2020-06-29 19:06:30Z

1

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)

answered Jun 29, 2020 at 19:06

tachko

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Comments

EugenSunic · Accepted Answer · 2020-06-29 19:07:24Z

1

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)

answered Jun 29, 2020 at 19:07

EugenSunic

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