Create a New Index Array

Question

Not sure why this isn't working.

Instructions:

// Create a function called indexFinder that will loop over an array and return a new array of the indexes of the contents e.g. [243, 123, 4, 12] would return [0,1,2,3]. Create a new variable called 'indexes' and set it to contain the indexes of randomNumbers.

Tried Solution:

let randomNumbers = [1, 3453, 34, 456, 32, 3, 2, 0];
let indexes = [];

function indexFinder(arr){
  for(var i = 0; arr.length; i++){
    indexes.push(i);
  }

  return indexes;
}

indexFinder(randomNumbers);
console.log(indexes);

CertainPerformance · Accepted Answer · 2018-05-04 23:54:44Z

2

You have no real condition test in your for loop because arr.length, when above 0, is always truthy.

let randomNumbers = [1, 3453, 34, 456, 32, 3, 2, 0];
let indexes = [];

function indexFinder(arr){
  for(var i = 0; i < arr.length; i++){
    indexes.push(i);
  }

  return indexes;
}

indexFinder(randomNumbers);
console.log(indexes);

But there's a much more concise way of doing this:

const randomNumbers = [1, 3453, 34, 456, 32, 3, 2, 0];
const indexFinder = arr => arr.map((_, i) => i);
console.log(indexFinder(randomNumbers));

answered May 4, 2018 at 23:54

CertainPerformance

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1 Comment

user2437417 Over a year ago

Or Object.keys(arr) ...though I guess they'd be strings, so Object.keys(arr).map(Number)

sumit · Accepted Answer · 2018-05-05 00:09:07Z

2

Another method is using Array.from

const randomNumbers = [1, 3453, 34, 456, 32, 3, 2, 0];
console.log(Array.from(randomNumbers, x => randomNumbers.indexOf(x)));

Or we can use keys

const randomNumbers = [1, 3453, 34, 456, 32, 3, 2, 0];
console.log([...Array(randomNumbers.length).keys()])

edited May 5, 2018 at 0:09

answered May 5, 2018 at 0:01

sumit

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Comments

Ele · Accepted Answer · 2018-05-05 00:02:41Z

1

The problem is the condition within that for-loop using just arr.length because for length greater than 0 will be always true.

An alternative is using the function Array.from:

let randomNumbers = [1, 3453, 34, 456, 32, 3, 2, 0],
    indexes = Array.from({length: randomNumbers.length}, (_, i) => i);
    
console.log(indexes);

Another alternative is getting the length and then execute a simple for-loop.

answered May 5, 2018 at 0:02

Ele

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