Remove entry from array using another array

Question

Not sure how do to this, so any help is greatly appreciated

Say I have :

const array1 = [1, 1, 2, 3, 4];
const array2 = [1, 2];

Desired

Answer 1

If you are going to work with large arrays, this solution will perform very well. First convert array1 to a Map to make your lookups quick. Then go through array2 and subtract from your map to signify that the element should get removed. Then finally run through your map and add the keys that have values bigger than 0

const array1 = [1, 1, 2, 3, 4];
const array2 = [1, 2];

const obj = array1.reduce((acc, cv) => {
    if (acc.has(cv)) acc.set(cv, acc.get(cv) + 1);
    else acc.set(cv, 1);
    return acc;
}, new Map());

array2.forEach(i => {
    if (obj.has(i)) obj.set(i, obj.get(i) - 1);
});

const res = [];
obj.forEach((v, k) => { if (v) res.push(k); });
console.log(res)