JavaScript - Compare 2 arrays and return which are not present in both array

Question

I want to Compare 2 arrays arr1 and arr2. If an array of arr1 is not present in arr2 then I want the first element of that array.

const arr1 = [
  ["item 1", "item 1.1", "item 1.2"],
  ["item 2", "item 2.1", "item 2.2"],
  ["item 3", "item 3.1", "item 3.2"],
  ["item 4", "item 4.1", "item 4.2"],
];


const arr2 = [
  ["item 1", "item 1.1", "item 1.2"],
  ["item 2", "item 2.1", "item 2.2"],

];

const newArr = () => {
  return arr1.filter(arr => arr2.some(arr2 => arr2[0] != arr[0]))

};

console.log(newArr())

// Expected output [ 'item 3', 'item 4' ]

It is not so clear. what exactly do you want and what is your expected output? — DecPK
– DecPK, Commented Jun 3, 2021 at 8:18

DecPK · Accepted Answer · 2021-06-03 08:21:45Z

2

You can easily achieve this result using reduce and find.

const arr1 = [
  ["item 1", "item 1.1", "item 1.2"],
  ["item 2", "item 2.1", "item 2.2"],
  ["item 3", "item 3.1", "item 3.2"],
  ["item 4", "item 4.1", "item 4.2"],
];

const arr2 = [
  ["item 1", "item 1.1", "item 1.2"],
  ["item 2", "item 2.1", "item 2.2"],
];

const result = arr1.reduce((acc, curr) => {
  const [first] = curr;
  const isExist = arr2.find((nestedArray) => nestedArray[0] === first);
  if (!isExist) acc.push(first);
  return acc;
}, []);

console.log(result);

answered Jun 3, 2021 at 8:21

DecPK

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1 Comment

DecPK Over a year ago

@mplungjan forgot to console.log. Thanks for pointing out.

Win · Accepted Answer · 2021-06-03 08:31:45Z

1

If you're working with large arrays, I would recommend you stringify them for comparison like the example code below.

const arr1 = [
  ["item 1", "item 1.1", "item 1.2"],
  ["item 2", "item 2.1", "item 2.2"],
  ["item 3", "item 3.1", "item 3.2"],
  ["item 4", "item 4.1", "item 4.2"]
];

const arr2 = [
  ["item 1", "item 1.1", "item 1.2"],
  ["item 2", "item 2.1", "item 2.2"]
];

const notMatchingItems = [];

for (var i = 0; i < arr1.length; i++) {
  if (JSON.stringify(arr1[i]) !== JSON.stringify(arr2[i])) {
    notMatchingItems.push(arr1[i][0]);
  }
}

console.log(notMatchingItems);

answered Jun 3, 2021 at 8:31

Win

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