Difference between two array when elements are array

Question

var a = [["Green","Medium"],["Green","Small"],["Medium","Red"],["Red","Small"]];

var b = [["Green","Medium"],["Green","Small"],["Medium","Red"]];

So my result will [["Red","Small"]]

Not that a.filter(x => !b.includes(x)) won't work because all element are array. I've tried something like that

    var diff = [];
    a.forEach((res, i) => {
      b.forEach((res2, j) => {
        if (i === j && !_.isEqual(res, res2)) {
          diff.push(res);
        }
      });
    });
console.log(diff);

This not working when different elements are last positions

Will `a` always contain more (or the same) elements as `b`? – CertainPerformance Dec 27 '18 at 05:32 — CertainPerformance, Dec 27 '18 at 05:32

score 3 · Answer 1 · answered Dec 27 '18 at 05:37

In lodash, you can use _.differenceWith() and supply _.isEqual() as a comparator to perform a deep comparison:

const c = _.differenceWith(a, b, _.isEqual);

Full snippet:

const a = [["Green","Medium"],["Green","Small"],["Medium","Red"],["Red","Small"]];
const b = [["Green","Medium"],["Green","Small"],["Medium","Red"]];

const c = _.differenceWith(a, b, _.isEqual);

console.log(c);

<script src="https://cdnjs.cloudflare.com/ajax/libs/lodash.js/4.17.11/lodash.min.js"></script>

score 2 · Accepted Answer · answered Dec 27 '18 at 05:35

For an O(N) solution that doesn't require a library, I'd map b to a Set of strings by stringifying the contents of each sub-array, then filter a by whether a's stringified items are contained in the set:

var a = [["Green","Medium"],["Green","Small"],["Medium","Red"],["Red","Small"]];
var b = [["Green","Medium"],["Green","Small"],["Medium","Red"]];

const bSet = new Set(b.map(arr => JSON.stringify(arr)));
const aFiltered = a.filter(arr => !bSet.has(JSON.stringify(arr)));
console.log(aFiltered);

(Set.has is generally O(1), unlike Array methods like includes and indexOf)

Yes. I like this technique without lodash. Thank you – Imran Dec 27 '18 at 10:06 — Imran, Dec 27 '18 at 10:06

score 2 · Answer 3 · answered Dec 27 '18 at 05:37

As you are already using lodash you can use combination of filter and every to compare two array.

var a = [["Green","Medium"],["Green","Small"],["Medium","Red"],["Red","Small"]];

var b = [["Green","Medium"],["Green","Small"],["Medium","Red"]];


var unique = a.filter(a=> b.every(b=> !_.isEqual(a, b)));
console.log(unique)

<script src="https://cdnjs.cloudflare.com/ajax/libs/lodash.js/4.17.4/lodash.js"></script>

score 0 · Answer 4 · answered Dec 27 '18 at 05:38

var a = [["Green","Medium"],["Green","Small"],["Medium","Red"],["Red","Small"]];

var b = [["Green","Medium"],["Green","Small"],["Medium","Red"]];

var c = b.map(ele=>JSON.stringify(ele));

var p = a.filter(ele=>!c.includes(JSON.stringify(ele)))

console.log(p)

Difference between two array when elements are array

4 Answers4