Add Parent Property to each Objects using FlatMap/Map-CodePudding

I am trying to achieve the following results in few lines of code.

Expected Result:

[{
  active: true,
  id: 1,
  name: "California",
  country: USA
}, {
  active: true,
  id: 2,
  name: "New York",
  country:"USA"
},...
 {
  active: true,
  id: 4,
  name: "Moscow",
  country:"Russia"
}, ....]

This is what I tried but again there is a property country missing in the results. Expecting the shortest & efficient way to achieve this. Thank you for your responses.

 const obj = [
    {
      country: "USA",
      cities: ["California", "New York", "Austin"]
    },
    {
      country: "Russia",
      cities: ["Moscow", "kazan", "Samara"]
    }
  ];
 
//here the map of country is not there, wondering how to achieve this.
//obj.map(y => y.country).flatMap(x => x.cities)
const aa = obj.flatMap(x => x.cities)
   .map((str, index) => ({ name: str, id: index   1, active:true}));

console.log(aa)

CodePudding user response：

The problem with Behram's and Ori's above is that the generated index is not correct; it will generate 1,2,3,1,2,3:

Instead remove the index value from the mappers:

let index = 1;
const results = obj.flatMap(({ country, cities }) => cities.map((city) => ({ active: true, id: index  , name: city, country })));

console.log(result)

CodePudding user response：

You'll need another .map to tie each city with its country first.

const obj = [
    {
      country: "USA",
      cities: ["California", "New York", "Austin"]
    },
    {
      country: "Russia",
      cities: ["Moscow", "kazan", "Samara"]
    }
  ];
  
const aa = obj
  .flatMap(({ cities, country }) => cities.map(city => ({ name: city, country })))
  .map((obj, index) => ({ ...obj, id: index   1, active:true}));

console.log(aa)

You might consider the imperative version too. While less functional, it's a bit easier to understand.

const obj = [
    {
      country: "USA",
      cities: ["California", "New York", "Austin"]
    },
    {
      country: "Russia",
      cities: ["Moscow", "kazan", "Samara"]
    }
  ];
const aa = [];
let id = 1;
for (const { cities, country } of obj) {
  for (const name of cities) {
    aa.push({ name, country, id: id  , active: true });
  }
}
console.log(aa)

CodePudding user response：

  function transform(obj) {
      let id = 0;
      return obj.flatMap(({country, cities}) => cities.map(city => ({active:true, name: city, country,id:   id})))
  }
  
 console.log(transform(obj))

if you want a one-liner you can store that id in a parent anonymous function, ( but I will not suggest this as this is less readable )

 console.log(((id) => obj.flatMap(({country, cities}) => cities.map(city => ({active:true, name: city, country,id:   id}))))(0))

CodePudding user response：

follow this way:

const results = obj.flatMap(({ country, cities }) => {
    return cities.map((city, index) => ({
        active: true,
        id: index   1,
        name: city,
        country: country
    }));
});
console.log(results);