JavaScript return array of keys that are all empty in array of objects

Question

I have an array of objects

const arrayOfObjects = [{firstKey: '', secondKey: 'someValue', thirdkey: 'someValue', fourthKey: ''},{firstKey: '', secondKey: '', thirdkey: 'someValue', fourthKey: ''}];

I need to return an array of keys that are empty in all of the objects in the array. So for the above example, it would return ['firstKey', 'fourthKey'] but not 'secondKey', because it is only empty in one of the objects.

I have found a lot of examples (like one below) that return boolean but having trouble finding a way to return the actual empty keys. Thanks

const isEmpty = Object.values(object).every(x => (x === ''));

I guess, you just need a filter over here. Rather than making it complicated by using every and then x === '' — Himanshu Saxena
– Himanshu Saxena, Commented May 6, 2021 at 19:47

Ori Drori · Accepted Answer · 2021-05-06 21:04:05Z

2

Get the keys from the 1st object in the array, and then filter them by checking for each key that it's empty in all objects with Array.every():

const checkAllEmpty = arr =>
  Object.keys(arr[0] ?? {}) // get the keys from the 1st object or use an empty object as fallback
    .filter(key => arr.every(o => o[key] === '')) // filter the keys by checking each object in the array

const arr = [{firstKey: '', secondKey: 'someValue', thirdkey: 'someValue', fourthKey: ''},{firstKey: '', secondKey: '', thirdkey: 'someValue', fourthKey: ''}]

const result = checkAllEmpty(arr)

console.log(result)

Old answer:

Reduce the array to a Map, and count how many times a key is empty. Convert the Map to an an array of [key, value] using Array.from(), filter all the entries that have a value that is less then the array's length, and map to an array of keys:

const arr = [{firstKey: '', secondKey: 'someValue', thirdkey: 'someValue', fourthKey: ''},{firstKey: '', secondKey: '', thirdkey: 'someValue', fourthKey: ''}]

const result = Array.from(arr.reduce((acc, obj) => {
    Object.entries(obj)
      .forEach(([k, v]) => {
        if (v === '') acc.set(k, (acc.get(k) ?? 0) + 1)
      })

    return acc
  }, new Map))
  .filter(([, v]) => v === arr.length)
  .map(([k]) => k)

console.log(result)

edited May 6, 2021 at 21:04

answered May 6, 2021 at 20:00

Ori Drori

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1 Comment

Ori Drori Over a year ago

@Marky1298 - I've updated the answer with a better solution.

Guerric P · Accepted Answer · 2021-05-06 19:53:25Z

1

Array.prototype.every returns true when every item satisfies the predicate you pass as a callback. What you actually need is Array.prototype.filter:

const arrayOfObjects = [{firstKey: '', secondKey: 'someValue', thirdkey: 'someValue', fourthKey: ''},{firstKey: '', secondKey: '', thirdkey: 'someValue', fourthKey: ''}];

const deduplicate = arr => [...new Set(arr)];

const isEmpty = arrayOfObjects.flatMap(x => Object.entries(x)).filter(([, value]) => !value).map(([key]) => key);

const uniqueIsEmpty = deduplicate(isEmpty);

console.log(uniqueIsEmpty);

edited May 6, 2021 at 19:53

answered May 6, 2021 at 19:47

Guerric P

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2 Comments

Marky1298 Over a year ago

Thanks, this is close, I would just need to make each key unique and only key (not value) in return. Thanks, will work with this

Marky1298 Over a year ago

Yes, thanks "it would return [firstKey, fourthKey] but not secondKey, because it is only empty in one of the objects"

Neobyte · Accepted Answer · 2021-05-06 23:33:35Z

1

This version will assume undefined keys are also "empty", in case the objects in your array have inconsistent keys.

const arr = [
    {firstKey: '', secondKey: 'someValue', thirdkey: 'someValue', fourthKey: ''}, 
    {firstKey: '', secondKey: '', thirdkey: 'someValue', fourthKey: ''}
];

const isEmpty = v => v == '';

const result = Array.from(
    arr.reduce((acc, obj) => 
        Object.entries(obj).reduce((_, [k, v]) => 
            acc.set(k, acc.has(k) ? acc.get(k) && isEmpty(v) : isEmpty(v))
        , null)
    , new Map())
).filter(([, v]) => v).map(([k]) => k);

console.log(result)

answered May 6, 2021 at 23:33

Neobyte

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Comments

Kinglish · Accepted Answer · 2021-05-06 19:49:28Z

0

const arrayOfObjects = [{firstKey: '', secondKey: 'someValue', thirdkey: 'someValue', fourthKey: ''},{firstKey: '', secondKey: '', thirdkey: 'someValue', fourthKey: ''}];
let k = []
arrayOfObjects.map(obj => { k = k.concat(k, Object.keys(obj))})
let arr = [...new Set(k)];
console.log(arr);

answered May 6, 2021 at 19:49

Kinglish

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