Object filter by N highest numeric values (of keys)

Question

Demo Object:

var foo = {a:1, b:2, c:3, d:4, e:5, f:6, g:7}

Wanted result: (get top 3 keys by value)

{e:5, f:6, g:7}

---

Explanation:

For a given key/value basic object, how would you get the 3 top values, but not just the values but also the keys? keys could be anything. lets say values are integers.

performance should be in mind.

Answer 1

You can extract the properties into an array, then sort the array:

var foo = {a:1, b:2, c:3, d:4, e:5, f:6, g:7}
var props = Object.keys(foo).map(function(key) {
  return { key: key, value: this[key] };
}, foo);
props.sort(function(p1, p2) { return p2.value - p1.value; });
var topThree = props.slice(0, 3);

If you want the result as an object, just reduce it back to one

var topThreeObj = props.slice(0, 3).reduce(function(obj, prop) {
  obj[prop.key] = prop.value;
  return obj;
}, {});

Answer 2

Get key/value pairs:

let pairs = Object.entries(foo);

Sort them:

pairs.sort((a, b) => a[1] - b[1]);

Turn some back into an object:

let result = Object.fromEntries(pairs.slice(-3));