How to extract multi-property duplicates from an array of objects?

Question

I have an array of objects where properties may share the same values:

const arr = [
  {name: 'Stephan', phone: 123},
  {name: 'Stephan', phone: 432},
  {name: 'Begal', phone: 432},
  {name: 'Lucy', phone: 777},
  {name: 'Angel', phone: 432},
  {name: 'Lucy', phone: 555},
  {name: 'Mike', phone: 999},
];

(You can observe that either the name or the phone can be repeated more than once).

I need to extract the objects that have duplicated phone/name in a separate array/object for further manipulation.

Ideally, the array of duplicates generated from the example above could look like this:

const dups = [
  [
    {name: 'Stephan', phone: 123},
    {name: 'Stephan', phone: 432},
    {name: 'Begal', phone: 432},
    {name: 'Angel', phone: 432},
  ],
  [
    {name: 'Lucy', phone: 777},
    {name: 'Lucy', phone: 555},
  ]
];

How can achieve that?

My algorithm knowledge is not strong, but I imagine that sorting the original array by both name and phone would be the first step?

georg · Accepted Answer · 2016-09-09 20:34:54Z

1

No need to sort. Iterate the array and maintain two helper indexes that say "name/phone X is in the group Y":

const arr = [
    {name: 'Stephan', phone: 123},
    {name: 'Stephan', phone: 432},
    {name: 'Begal', phone: 432},
    {name: 'Lucy', phone: 777},
    {name: 'Angel', phone: 432},
    {name: 'Lucy', phone: 555},
    {name: 'Mike', phone: 999},
];


var groups = [[]],
    names = {},
    phones = {};

for (var obj of arr) {
    var g = names[obj.name] || phones[obj.phone];
    if (!g)
        groups[g = groups.length] = [];
    groups[g].push(obj);
    names[obj.name] = phones[obj.phone] = g;
}

console.log(groups.slice(1))

answered Sep 9, 2016 at 20:34

georg

216k57 gold badges324 silver badges401 bronze badges

Sign up to request clarification or add additional context in comments.

3 Comments

marzelin Over a year ago

Why did you initially add an empty array here var groups = [[]]?

georg Over a year ago

@marzelin: just to make the !g check simpler (otherwise I'd have to check for undefineds).

marzelin Over a year ago

Yeah, 0 is a falsy value. Clever.

Collectives™ on Stack Overflow

How to extract multi-property duplicates from an array of objects?

1 Answer 1

3 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

3 Comments

Your Answer

Sign up or log in

Post as a guest

Related