Generate an array of identifiers from a pre-existing array

Question

Generate an array of identifiers from a pre-existing array

I am facing a challenge where I need to create an array of IDs for each element in an existing array whose size is unknown. The twist here is that every set of four elements should have the same ID.

As an illustration, if the original array (let's call it array1) contains 20 items, the new array would look like this: [1, 1, 1, 1, 2, 2, 2, 2, 3, 3, 3, 3, 4, 4, 4, 4, 5, 5, 5, 5]

I attempted to achieve this using a for loop but struggled with how to assign IDs to every four elements without overriding them during iteration.

for(let i = 0; i < itemlist.length; i++) {newArray[i] = i; newArray[i] = i;newArray[i] = i;newArray[i] = i;}

javascript arrays typescript

Answer 1

Answer №1

You can transform the current array by applying a function that generates unique IDs based on the index position in the original array

const someArray = [1,2,3,4,5,6,7,8,9,0,1,2,3,4,5,6,7,8,9,0];
const yourArray = someArray.map((el, i) => Math.floor(i / 4) + 1);

console.log(yourArray);

Answer 2

You can transform the current array by applying a function that generates unique IDs based on the index position in the original array

const someArray = [1,2,3,4,5,6,7,8,9,0,1,2,3,4,5,6,7,8,9,0];
const yourArray = someArray.map((el, i) => Math.floor(i / 4) + 1);

console.log(yourArray);

Answer 3

Answer №2

To efficiently create an array with only a quarter of the size, you can utilize the flatMap method to populate it with four elements per index.

function buildArray(size){
  return [...Array(size / 4)].flatMap((_,i)=>Array(4).fill(i + 1));
}
console.log(buildArray(20));

Answer 4

To efficiently create an array with only a quarter of the size, you can utilize the flatMap method to populate it with four elements per index.

function buildArray(size){
  return [...Array(size / 4)].flatMap((_,i)=>Array(4).fill(i + 1));
}
console.log(buildArray(20));

Generate an array of identifiers from a pre-existing array

Answer №1

Answer №2

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