Can you close empty gaps between array indices in JavaScript?

WillWillington 0
Viewed 29

I have an algorithm where some array will be given a new index, but the new index is not sequential. For the sake of time, just assume the new index is given to the array at random. Let's say I have this array:

const arr = [];
arr[5] = 'a'
arr[2] = 'b'
arr[9] = 'c'
arr[0] = 'd'

If I console.log this array to the output window, I get this:

['d', empty, 'b', empty × 2, 'a', empty × 3, 'c']

I'm wondering if it's possible to close/remove those empty gaps between values so the array entries are sorted by their actual index, so I can get this output:

['d', 'b', 'a', 'c']

Is there a short and easy way to do this?

indices sorting arrays javascript
2 Answers

You can just use Array.prototype.filter and filter out undefined values. You can take a shortcut by coercing them into boolean using the !! operator:

arr.filter(x => !!x);

This check is loose/dirty because anything falsy will be coerced to false, e.g. the numeric 0. If you really want to be strict and only filter out undefined, then you need a stricter predicate:

array.filter(x => typeof x !== 'undefined');


const arr = [];
arr[5] = 'a';
arr[2] = 'b';
arr[9] = 'c';
arr[0] = 'd';

console.log(arr);
console.log(arr.filter(x => !!x));
console.log(arr.filter(x => typeof x !== 'undefined'));

userg1F10

simply use Array.splice() method to "clean up" your array, wthiut creating a new one.

need to use reverse index progression

const arr = [];
arr[5] = 'a';
arr[2] = 'b';
arr[9] = 'c';
arr[0] = 'd';

console.log(JSON.stringify(arr));

for (let i=arr.length; i-- > 0;) 
  {
  if (arr[i]===undefined) arr.splice(i,1);
  }
  
console.log(JSON.stringify(arr));

Mister Jojo0
Related