merging specific object values from array into separated array

Question

I have this array of persons

personsList = [
  {cities: ['A', 'B', 'C']},
  {cities: ['A', 'B', 'C']},
  {cities: ['A', 'B', 'C']},
  {cities: ['A', 'B', 'C', 'D']}
]

in every object inside there more details beside cities but I want to make an array with all the cities inside - unique. so the result will be ['A', 'B', 'C', 'D']

I tried doing something like

const allCities = personsList.map(p => p.cities)

but then I got an array of arrays, what is the best approach for this one ? thanks.

p.cities is also array inner map function then use filter

Janaka Dissanayake
– Janaka Dissanayake

2018-05-23 07:14:20 +00:00
Commented May 23, 2018 at 7:14 — Janaka Dissanayake
– Janaka Dissanayake, Commented May 23, 2018 at 7:14

Nikhil Aggarwal · Accepted Answer · 2018-05-23 07:13:54Z

2

You can try following using Set

var personsList = [
  {cities: ['A', 'B', 'C']},
  {cities: ['A', 'B', 'C']},
  {cities: ['A', 'B', 'C']},
  {cities: ['A', 'B', 'C', 'D']}
]
 
// cities will have all the cities with duplicates
const allCities = personsList.reduce((a,c) => [...a, ...c.cities], []);
// create set from array - removes duplicate and then create array back from set
console.log(Array.from(new Set(allCities)));

answered May 23, 2018 at 7:13

Nikhil Aggarwal

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Comments

Hassan Imam · Accepted Answer · 2018-05-23 07:15:41Z

0

You can array#map all cities and then concat them into one array. Then using Set you can get the unique city.

const personsList = [ {cities: ['A', 'B', 'C']}, {cities: ['A', 'B', 'C']}, {cities: ['A', 'B', 'C']}, {cities: ['A', 'B', 'C', 'D']} ],
      uniqueCity = Array.from(new Set([].concat(...personsList.map(({cities}) => cities))));
console.log(uniqueCity);

answered May 23, 2018 at 7:15

Hassan Imam

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3 Comments

greW Over a year ago

Thanks, for the reply @Hassan, how do I run trim() on each city ?

Hassan Imam Over a year ago

Then you can use array#map. uniqueCity.map(city => city.trim());

greW Over a year ago

but then I'll have duplicate between A and A in the final array

Nina Scholz · Accepted Answer · 2018-05-23 07:15:01Z

0

You could use directly a Set for getting unique values.

var personsList = [{ cities: ['A', 'B', 'C'] }, { cities: ['A', 'B', 'C'] }, { cities: ['A', 'B', 'C'] }, { cities: ['A', 'B', 'C', 'D'] }],
    unique = Array.from(
        personsList.reduce(
            (s, { cities }) => cities.reduce((t, c) => t.add(c), s),
            new Set
        )
    );

console.log(unique);

answered May 23, 2018 at 7:15

Nina Scholz

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1 Comment

korona Over a year ago

var isn't technically deprecated, but I definitely think it should be avoided in all modern JavaScript

Християн Христов · Accepted Answer · 2018-05-23 07:19:08Z

0

I think this is the effect that you are looking for, by using set you guarantee yourself that there are only unique elements.

let personsList = [
  {cities: ['A', 'B', 'C']},
  {cities: ['A', 'B', 'C']},
  {cities: ['A', 'B', 'C']},
  {cities: ['A', 'B', 'C', 'D']}
]
const allCities = personsList.reduce((acc,e) => {
  e.cities.map(x=>{
  acc.add(x)
  })
  return acc
}, new Set())
console.log(Array.from(allCities))

answered May 23, 2018 at 7:19

Християн Христов

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Comments

Akhil Karthikeyan · Accepted Answer · 2018-05-23 08:31:15Z

0

const personsList = [
  { cities: ['A', 'B', 'C'] },
  { cities: ['A', 'B', 'C'] },
  { cities: ['A', 'B', 'C'] },
  { cities: ['A', 'B', 'C', 'D'] }
];
const allCities = [...new Set([].concat(...personsList.map(({ cities }) => cities)))];
console.log(allCities);

edited May 23, 2018 at 8:31

answered May 23, 2018 at 7:51

Akhil Karthikeyan

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