Compare objects containing arrays

Question

I have two JS objects which contain some arrays. I'd like to compare the two objects and create a third object, containing arrays only unique to secondObj.

They look like this:

firstObj : {
    Jim_Array : [...],
    Joe_Array : [...],
    Bill_Array : [...]
}

secondObj : {
    Bill_Array : [...],
    Sam_Array : [...],
    Kate_Array : [...],
    Jim_Array : [...],
    Joe_Array : [...]
}

I'd like to compare the two objects and end up with the following:

thirdObj : {
    Sam_Array : [...],
    Kate_Array : [...]
}

Possible duplicate of [Simplest code for array intersection in javascript](http://stackoverflow.com/questions/1885557/simplest-code-for-array-intersection-in-javascript) — Philip Raath, Jun 21 '16 at 14:31

score 2 · Accepted Answer · answered Jun 21 '16 at 14:21

You can try something like following

var thirdObj = {};
for (var key in secondObj) {
  if(!firstObj.hasOwnProperty(key)) {
     // In case you need to compare the array additional check will come here
     thirdObj[key] = secondObj[key];

  }

}

Another way

var thirdObj = {};
for (var key in secondObj) {
  if(firstObj[key] === undefined) {
     // In case you need to compare the array additional check will come here
     thirdObj[key] = secondObj[key];

  }

}

The first option is very similar to something I was working on, but better. Thanks, I appreciate the help. — Daft, Jun 21 '16 at 14:26

score 2 · Answer 2 · answered Jun 21 '16 at 14:27

You can use Object.keys() with reduce() and check if firstObj has property of secondObj with hasOwnProperty(), if not add to new object.

var firstObj = {Jim_Array : ['...'], Joe_Array : ['...'], Bill_Array : ['...']}
var secondObj = {Bill_Array : ['...'], Sam_Array : ['...'], Kate_Array : ['...'], Jim_Array : ['...'], Joe_Array : ['...']}

var result = Object.keys(secondObj).reduce(function(o, e) {
  if(!firstObj.hasOwnProperty(e)) o[e] = secondObj[e];
  return o;
}, {});

console.log(result)

score 1 · Answer 3 · answered Jun 21 '16 at 17:15

1

A solution using underscore:

var result = _.pick(secondObj, _.difference( _.keys(secondObj), _.keys(firstObj)));

answered Jun 21 '16 at 17:15

Gruff Bunny

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Compare objects containing arrays

3 Answers3