CODEWITHSUNDEEP
javascript
ndemasie
ndemasie

Reputation: 610

Loop through array multiple times

How do I repeat the colors array in order, given an unknown length of items?

const items = [1, 2, ...n]
const colors = ['blue', 'green', 'red']

// return ['blue', 'green', 'red', 'blue', 'green'] where items.length = 5

Upvotes: 4

Views: 2121

Answers (6)

Mohsen Alyafei
Mohsen Alyafei

Reputation: 5547

Using map()

const  items  = [1, 2, 3, 4, 5, 6, 7, 8],
       colors = ['blue', 'green', 'red'];
output = items.map((_,i) => colors[i % colors.length])
     
console.log(output);

Upvotes: 1

Cagri Tacyildiz
Cagri Tacyildiz

Reputation: 17590

You can take mode for index so you can repeat it.

const items = [1, 2, 3,4,5,6];
const colors = ['blue', 'green', 'red'];

var result=[];
items.forEach(myFunction)

function myFunction(item, index) {
  console.log(colors[(index%colors.length)])
  result.push(colors[(index%colors.length)])
}

Upvotes: 2

Nina Scholz
Nina Scholz

Reputation: 386560

Create a new array and map the values by using the remainder operator %.

const
    items = [1, 2, 3, 4, 5, 6, 7, 8],
    colors = ['blue', 'green', 'red'],
    result = Array.from(items, (_, i) => colors[i % colors.length]);

console.log(result);

Upvotes: 3

trincot
trincot

Reputation: 350167

When the target size is large, you may get better performance by doubling the array over and over again:

function stretch(arr, n) {
  while (arr.length < n) arr = arr.concat(arr);
  return arr.slice(0, n);
}

const items = [1, 2, 3, 4, 5];
const colors = ['blue', 'green', 'red'];

console.log(stretch(colors, items.length));

Upvotes: 3

Unmitigated
Unmitigated

Reputation: 89224

You can map over a new array with the length you want and take the modulus of the index by the length of the colors array. You do not seem to need the items array at all.

let len = 5;
const colors = ['blue', 'green', 'red'];
const res = Array(len).fill().map((_,idx)=>colors[idx % colors.length]);
console.log(res);

Array.from can also be used in this case.

let length = 5;
const colors = ['blue', 'green', 'red'];
const res = Array.from({length}, (_,idx)=>colors[idx % colors.length]);
console.log(res);

Upvotes: 3

Ali Faris
Ali Faris

Reputation: 18592

const items = [1, 2, 3,4,5,6,7,8]
const colors = ['blue', 'green', 'red']

const result = items.map((_,i) => colors[i%colors.length]);

console.log(result);

Upvotes: 7

Related Questions