Extract object from object array

Question

I need to split an object array into two variables. The first variable (main) should get the object with a title. The second one (content) should get all other objects.

Sample data

[
  { _id: '1', title: 'Main' },
  { _id: '2', foo: 'bar' },
  { _id: '2', foo: 'bar' }
]

I did it withfind()/filter() commands, but is it really necessary to find twice?

const main = data.find(doc => doc.title)
const content = data.filter(doc => !doc.title)

Is it possible to extract the main object instead of finding it?

I’m not sure what you mean by “extract the main object instead of finding it”. How would “extracting” look like if it’s not just “finding”? Other than that, your current solution already seems quite elegant. I’m not sure how it could be improved significantly. — Sebastian Simon
– Sebastian Simon, Commented Jan 23, 2018 at 15:26
Assuming you actually mean data.filter on the second line, I don't think there is anything wrong with it. Unless your array is huge there won't be any performance difference. And your current solution is much more readable than some other approaches. — str
– str, Commented Jan 23, 2018 at 15:31
Trivial with lodash let {false: docs, true: [main]} = _.groupBy(ary, x => !!x.title) — georg
– georg, Commented Jan 23, 2018 at 15:58

Nina Scholz · Accepted Answer · 2018-01-23 15:31:21Z

2

You could take a single loop approach and an object for same named arrays with a check if the property exist with in operator.

var data = [{ _id: '1', title: 'Main' }, { _id: '2', foo: 'bar' }, { _id: '2', foo: 'bar' }],
     main = [],
     content = [],
     temp = { main, content };

data.forEach(doc => temp['title' in doc ? 'main' : 'content'].push(doc));

console.log(main);
console.log(content);

.as-console-wrapper { max-height: 100% !important; top: 0; }

With just one object with title, you could assign the object directly and collec the other objects in an array.

var data = [{ _id: '1', title: 'Main' }, { _id: '2', foo: 'bar' }, { _id: '2', foo: 'bar' }],
     main,
     content = [];

data.forEach(doc => 'title' in doc
    ? main = doc
    : content.push(doc)
);

console.log(main);
console.log(content);

.as-console-wrapper { max-height: 100% !important; top: 0; }

edited Jan 23, 2018 at 15:31

answered Jan 23, 2018 at 15:22

Nina Scholz

388k26 gold badges367 silver badges417 bronze badges

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

2 Comments

user3142695 Over a year ago

Would it be possible to have main as an object - as it is aways only one object?

Nina Scholz Over a year ago

@user3142695, yes it is possible, take example two.

Jeremy Thille · Accepted Answer · 2018-01-23 15:20:58Z

0

const content = data.find(doc => !doc.title)

This doesn't work, because find returns one object only (the first found), not all the objects that don't match the condition. You'll have to use a filter for that

const content = data.filter(doc => !doc.title)

So yes, you'll have to iterate twice, one time to find the matching object, and a second time to build an array excluding the matching object.

answered Jan 23, 2018 at 15:20

Jeremy Thille

26.4k12 gold badges48 silver badges64 bronze badges

Comments

Andrei Todorut · Accepted Answer · 2018-01-23 15:22:18Z

0

var docs = [
  { _id: '1', title: 'Main' },
  { _id: '2', foo: 'bar' },
  { _id: '2', foo: 'bar' }
];

var doc = [],main = [];

for(_doc in docs){
    if(typeof docs[_doc].title != 'undefined') {
        doc.push(docs[_doc]);
        continue;
  }

  main.push(docs[_doc]);
}

Working fiddle: https://jsfiddle.net/andreitodorut/fcLkata6/

answered Jan 23, 2018 at 15:22

Andrei Todorut

4,5762 gold badges19 silver badges27 bronze badges

Comments

Scott Sauyet · Accepted Answer · 2018-01-23 16:13:13Z

0

I would do this a bit differently. The notion of partitioning a list by a predicate is worth extracting. So I might do this:

const docs = [{_id: '1', title: 'Main'},{_id: '2', foo: 'bar'},{_id: '2', foo: 'bar'}]

const partition = pred => data => data.reduce(
  ([matches, mismatches], item) => pred(item) 
     ? [matches.concat(item), mismatches]
     : [matches, mismatches.concat(item)],
  [[], []]
)

const withTitle = partition(doc => 'title' in doc)

console.log(withTitle(docs))

.as-console-wrapper { max-height: 100% !important; top: 0; }

Of course it's quite possible that withTitle should be inlined, if it's not being reused. It's also possible that the currying I put in, my usual default, is not necessary for you, and it should read (pred, data) => data.reduce(...)

edited Jan 23, 2018 at 16:13

answered Jan 23, 2018 at 15:59

Scott Sauyet

50.9k5 gold badges57 silver badges111 bronze badges

Collectives™ on Stack Overflow

Extract object from object array

4 Answers 4

2 Comments

Comments

Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

4 Answers 4

2 Comments

Comments

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related