let selected = [
  {id: 15, name: 'Canada'},
  {id: 25, name: 'Germany'}
];

let all = [
  {id: 15, name: 'Canada'},
  {id: 25, name: 'Germany'},
  {id: 32, name: 'United States'},
  {id: 40, name: 'China'}
]

How do I get non-selected countries from all objects and print it out in another variable? Based on id key of those which are in selected array?

let selected = [
  {id: 15, name: 'Canada'},
  {id: 25, name: 'Germany'}
];

let all = [
  {id: 15, name: 'Canada'},
  {id: 25, name: 'Germany'},
  {id: 32, name: 'United States'},
  {id: 40, name: 'China'}
]

How do I get non-selected countries from all objects and print it out in another variable? Based on id key of those which are in selected array?

• javascript
• ecmascript-6

• 1 Caveat, remember that {id: 25, name: 'Germany'} !== {id: 25, name: 'Germany'}. – Jared Smith Commented Feb 3, 2017 at 16:53

3 Answers 3

You need to find all objects that aren't contained in selected and then do something with them:

let nonSelectedItems = all.filter(obj => selected.every(s => s.id !== obj.id));

//do stuff with non-selected items

You can use filter and find, so as soon as element with same id is found in selected it will filter out that element from all. You can also use some instead of find.

let selected = [
  {id: 15, name: 'Canada'},
  {id: 25, name: 'Germany'}
];

let all = [
  {id: 15, name: 'Canada'},
  {id: 25, name: 'Germany'},
  {id: 32, name: 'United States'},
  {id: 40, name: 'China'}
]

var r = all.filter(e => !selected.find(a => e.id === a.id));
console.log(r)

Generate an object which holds id as a property using Array#reduce method(which helps to speed up since you need to iterate over and over) and use Array#filter method to filter elements from all array.

// generate the object reference
let ref = selected.reduce(function(obj, o) {
  // define property
  obj[o.id] = true;
  // return object property
  return obj;
  // set initial value as an object
}, {});

// filter out array elements
let res = all.filter(function(o) {
  return !ref[o.id]
})

let selected = [{
  id: 15,
  name: 'Canada'
}, {
  id: 25,
  name: 'Germany'
}];

let all = [{
  id: 15,
  name: 'Canada'
}, {
  id: 25,
  name: 'Germany'
}, {
  id: 32,
  name: 'United States'
}, {
  id: 40,
  name: 'China'
}]

let ref = selected.reduce(function(obj, o) {
  obj[o.id] = true;
  return obj;
}, {});

console.log(
  all.filter(function(o) {
    return !ref[o.id]
  })
)

With ES6 arrow function :

let ref = selected.reduce((obj, o) => (obj[o.id] = true, obj), {});

let res = all.filter(o => !ref[o.id]);

let selected = [{
  id: 15,
  name: 'Canada'
}, {
  id: 25,
  name: 'Germany'
}];

let all = [{
  id: 15,
  name: 'Canada'
}, {
  id: 25,
  name: 'Germany'
}, {
  id: 32,
  name: 'United States'
}, {
  id: 40,
  name: 'China'
}]

let ref = selected.reduce((obj, o) => (obj[o.id] = true, obj), {});

console.log(
  all.filter(o => !ref[o.id])
)