How to combine objects of arrays that are in different objects

Question

const all = [{
  'name': 'first',
  'attributes': [{
    'name': 'attr1'
  }]
}, {
  'name': 'second',
  'attributes': [{
    'name': 'attr2'
  }]
}]


const res = all.reduce((acc, el) => {
  return acc + el.attributes
}, [])

console.log(res)

I need get next

result => [{'name':'attr1'}, {'name':'attr2'}]

What is the best way do it, it can be not only reduce.

@evolutionxbox Because that would return an Array of Arrays. flatMap, though, would work — blex
– blex, Commented Dec 22, 2020 at 20:11

Barmar · Accepted Answer · 2020-12-22 20:08:34Z

3

Use the .concat() method to concatenate arrays, not +.

const all = [{
  'name': 'first',
  'attributes': [{
    'name': 'attr1'
  }]
}, {
  'name': 'second',
  'attributes': [{
    'name': 'attr2'
  }]
}]


const res = all.reduce((acc, el) => acc.concat(el.attributes), [])

console.log(res)

answered Dec 22, 2020 at 20:08

Barmar

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Comments

IvanD · Accepted Answer · 2020-12-22 20:13:38Z

1

You can also use spread operator for readability:

[...acc, ...el.attributes] means that it is a new array, in the beginning of which are all acc elements are placed, and after all el.attributes elements are placed.

The arrow function in reduce has no curly braces and the return keyword, in this form it returns [...acc, ...el.attributes]:

const all = [{
  'name': 'first',
  'attributes': [{
    'name': 'attr1'
  }]
}, {
  'name': 'second',
  'attributes': [{
    'name': 'attr2'
  }]
}]

  
const res = all.reduce((acc, el) => [...acc, ...el.attributes], [])

console.log(res)

answered Dec 22, 2020 at 20:13

IvanD

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Comments

blex · Accepted Answer · 2020-12-22 20:26:41Z

1

There's also flatMap:

const all = [{ name: 'first', attributes: [{ name: 'attr1' }] }, { name: 'second', attributes: [{ name: 'attr2' }] }];

const res = all.flatMap(x => x.attributes);

console.log(res);

edited Dec 22, 2020 at 20:26

answered Dec 22, 2020 at 20:16

blex

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Comments

tsu · Accepted Answer · 2020-12-22 20:14:28Z

0

One line code for you

[].concat(...all.map(item => item.attributes ))

answered Dec 22, 2020 at 20:14

tsu

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