Object.assign() and array of objects

Question

I have a nested array like this

const names= [[{name: "John"}, {name: "Mary"}],
           [{name: "Paul"}, {name: "Peter"}]];

I would like inject country into the nested object

const country = {country :"USA"}

so that output looks like

[{name: "John", country : "USA"}, {etc} ,{etc} ]

The code idea have is something like this

const combined = names.map((map)=> 
       Object.assign({}, 
              country, 
              /*something to extract name from nested array names*/),
       {country}
         )

Any suggestions how i could spread the object in the nested array to form the desired output?

If the code could be improved in other ways, please let me know as well

Should country be add to all array elements or just the first element in the nested array? — Dinesh Pandiyan
– Dinesh Pandiyan, Commented Nov 20, 2018 at 9:06
So you want to add another key to every object? But is the expected output a similarly nested array of objects or just a flat array of objects? And should the old objects and arrays be reused? And will the array be always nested exactly one level deep? — Robert
– Robert, Commented Apr 23, 2020 at 4:19

Mamun · Accepted Answer · 2018-11-20 09:23:47Z

5

You can use flat() to create a new array with all sub-array elements concatenated before using map() like the following way:

const names= [[{name: "John"}, {name: "Mary"}],
           [{name: "Paul"}, {name: "Peter"}]];
const country = {country :"USA"}
const combined = names.flat().map(p => Object.assign(p, country));
console.log(combined);

edited Nov 20, 2018 at 9:23

answered Nov 20, 2018 at 9:06

Mamun

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Comments

Shubham Khatri · Accepted Answer · 2018-11-20 09:11:12Z

2

Make use of reduce to flatten your array along with map and object.assign to add the country value to each object

const names= [[{name: "John"}, {name: "Mary"}],
           [{name: "Paul"}, {name: "Peter"}]];
const country = {country :"USA"};
const newNames = names.reduce((acc, item) =>{
    acc= acc.concat(item.map(value => Object.assign({}, value, country)));
    return acc;
},[]);
console.log(newNames);

answered Nov 20, 2018 at 9:11

Shubham Khatri

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Comments

Matías Fidemraizer · Accepted Answer · 2018-11-20 09:09:14Z

1

It's about using a nested map in an outer map:

const names = [
  [{
    name: "John"
  }, {
    name: "Mary"
  }],
  [{
    name: "Paul"
  }, {
    name: "Peter"
  }]
]

const country = { country: 'USA' }

const output = names.map (xs => xs.map (x => ({ ...x, ...country })))

console.log (output)

answered Nov 20, 2018 at 9:09

Matías Fidemraizer

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Comments

CertainPerformance · Accepted Answer · 2018-11-20 09:04:42Z

0

You might declare a new array literal, list country as the first item, then spread the names[0] array into it, no need for Object.assign nor .map if you only have one sub-array:

const names= [[{name: "John"}, {name: "Mary"}],
           [{name: "Paul"}, {name: "Peter"}]];
const country = {country :"USA"};
const newNames = [[country, ...names[0]]];
console.log(newNames);

answered Nov 20, 2018 at 9:04

CertainPerformance

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Dinesh Pandiyan · Accepted Answer · 2018-11-20 09:12:46Z

0

You can double map the names array and it's nested array and destructure country into each item.

const names = [[{name: "John"}, {name: "Mary"}],
           [{name: "Paul"}, {name: "Peter"}]];
           
const country = {country :"USA"};

const namesWithCountry = names.map(name => name.map(n => ({...n, ...country})));

console.log(namesWithCountry);

answered Nov 20, 2018 at 9:12

Dinesh Pandiyan

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Comments

Nick Parsons · Accepted Answer · 2020-01-31 02:15:24Z

0

You can use .flatMap() to flatten the arrays returned by the inner .map() method:

const names= [[{name: "John"}, {name: "Mary"}], [{name: "Paul"}, {name: "Peter"}]],
res = names.flatMap(arr => arr.map(elem => ({...elem, country: 'USA'})));

console.log(res);

edited Jan 31, 2020 at 2:15

answered Nov 20, 2018 at 9:12

Nick Parsons

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