javascript: 교집합(Union), 합집합(Intersection), 여집합(difference, minus)

• ECMAScript 6 sets: union, intersection, difference
• [itertools — Functions creating iterators for efficient looping](https://docs.python.org/3/library/itertools.html]

Union

let a = new Set([1,2,3]);
let b = new Set([4,3,2]);
let union = new Set([...a, ...b]);
    // {1,2,3,4}

Intersection

let a = new Set([1,2,3]);
let b = new Set([4,3,2]);
let intersection = new Set(
    [...a].filter(x => b.has(x)));
    // {2,3}

Difference

let a = new Set([1,2,3]);
let b = new Set([4,3,2]);
let difference = new Set(
    [...a].filter(x => !b.has(x)));

Choice Key

const o = {
  a: 'somestring',
  b: 42,
  c: 0,
  d: 1,
  e: 1,
  f: 1
};

keys = `a,b,c,d`;

//var obj = Object.fromEntries(Object.entries(o).filter(item=>keys.indexOf(item[0])>=0))
var obj = Object.fromEntries(Object.entries(o).filter(item=>keys.replace(/\s/g,"").split(",").includes(item[0])))
// { a: "somestring", b: 42, c: 0, d: 1 }