JavaScript - compare multiple arrays to one

Question

I would like to output which of 'buns' and 'duns' has the most elements in common with 'me'. How should I do this?

var buns = ['bap', 'bun', 'bop'];
var duns = ['dap', 'dun', 'dop'];

var me = ['dap', 'bun', 'bop'];

Answer 1

reduce over the array to be tested and check if each element is in me .

function common(arr1, arr2) {
  return arr2.reduce(function (p, c) {
    if (arr1.indexOf(c) > -1) p++;
    return p;
  }, 0);
}

common(me, buns); // 2
common(me, duns); // 1

DEMO

Answer 2

Index important

function hamd(a, b) {
    return a.reduce((sum, item, i) => {
        if (item !== b[i]) return sum + 1;
        return sum;
    }, 0);
}

Index not important, duplicates not important

function diff(a, b) {
    return a.reduce((sum, item, i) => {
        if (b.indexOf(item) === -1) return sum + 1;
        return sum;
    }, 0);
}

Index not important, duplicates important

function diffU(a, b) {
    b = b.slice();
    return a.reduce((sum, item, i) => {
        let i = b.indexOf(item);
        if (i === -1) return sum + 1;
        b.splice(i, 1);
        return sum;
    }, 0);
}

The one with the lowest score has the most similarity, eg

diff(me, buns) // 1
diff(me, duns) // 2
// `buns` is more like `me` than `duns`

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Please note that these are not commutative operations when the length of the Array is not the same; diff(a, b) may be different to diff(b, a) when a.length !== b.length
If you want to compare the results you need the common array on the same side of all tests