Comparing two arrays containing integers JavaScript

Question

I'm trying to compare two arrays.

firstArray has 451 integers in it, secondArray has 91 integers in it.

All integers that are in secondArray are also in firstArray.

I want to log out the integers from firstArray that are not in secondArray.

I tried the following :

 for (let i = 0; i < firstArray.length; i++) {
  for (let j = 0; j < secondArray.length; j++) {
     if (firstArray[i] !== secondArray[j]) {
       console.log(firstArray[i])
} } }

But it returned all 451 integers from the firstArray where I expected it to return 360 integers (firstArray - secondArray)

It's my first time posting here, hope it's clear enough ahah.

You said you tried it, did it work? what was happening that should not be happening? — Vladimir Mujakovic, Sep 02 '21 at 16:51
Hi Vladimir, it returned all 451 integers from the firstArray where I expected it to return 360 integers (firstArray - secondArray) — Adaen, Sep 02 '21 at 17:36
I have modified my original post, see if that works for you. — Vladimir Mujakovic, Sep 02 '21 at 18:26

Vladimir Mujakovic · Accepted Answer · 2021-09-02T18:29:19.627

-1

Use flags to keep track of which parts are in the set and which are not.

const arrOne = [34,2,12,4,76,7,8,9]
const arrTwo = [8,12,2]
let isInSet = false
const notInSet = []

// Expected output: 34, 4, 76, 7, 9

arrOne.forEach((el, i) => {
  isInSet = false
  arrTwo.forEach((curr, j) => {
    if (el == curr) {
      isInSet = true
    }
  })
  
  if (!isInSet) {
    notInSet.push(el)
  } 
})

console.log(notInSet)
// OR spread them out
console.log(...notInSet)

edited Sep 02 '21 at 18:29

answered Sep 02 '21 at 16:56

Vladimir Mujakovic

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This is just testing whether there's an element at the same index, not whether the elements are included. – Barmar Sep 02 '21 at 17:01
I misunderstood the original question, I have edited my post to reflect what was asked. @Barmar – Vladimir Mujakovic Sep 02 '21 at 18:24
Thank you so much ! It worked : ) – Adaen Sep 02 '21 at 19:09
You're welcome, if the response helped you feel free to mark it as an aswer. @Adaen – Vladimir Mujakovic Sep 02 '21 at 19:09

Comparing two arrays containing integers JavaScript

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