convert an array of objects to an object based on a given key

Question

I am new to Javascript.

I need to write a function to covert an array of objects to an object with a given key.

The input is like this

convert([{id: 1, value: 'abc'}, {id: 2, value: 'xyz'}], 'id')

and output needs to be like this

{
    '1': {id: 1, value: 'abc'},
    '2': {id: 2, value: 'xyz'}
}

I have tried the below code.

When I am trying this directly in console it seems it is working.

var arr = [{ id: 1, name: 'John', role: 'Developer'},
	   { id: 2, name: 'Jane', role: 'Lead'},
	   { id: 3, name: 'Robbie', role: 'QA'}];

let res = arr.reduce((prev, current) => {
  prev[current.v] = current;
  return prev;
}, {})

console.log(res)

But, when I am trying do it from the function it is not working.

function f(k, v) {
  //console.log(k);              
  k.reduce((prev, current) => {
    prev[current.v] = current;
    return prev;
    console.log(prev)
  }, {})
}

f(arr, 'role');

Any help will be highly appreciated.

Nina Scholz · Accepted Answer · 2019-03-30 08:53:06Z

2

You could take a dunctional approach by mapping an assigning new object.

function convert(array, key) {
    return Object.assign(...array.map(o => ({ [o[key]]: o })));
}


console.log(convert([{ id: 1, value: 'abc' }, { id: 2, value: 'xyz' }], 'id'))

answered Mar 30, 2019 at 8:53

Nina Scholz

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Comments

Mihai · Accepted Answer · 2019-03-30 08:54:24Z

1

This solution works for me:

function convert(obj, key) {
    var newObj = {};
    obj.forEach(element => {
        newObj[element[key]] = element;
    });
    return newObj;
}

var newObj = convert([{id: 1, value: 'abc'}, {id: 2, value: 'xyz'}], 'id');

console.log(newObj);

answered Mar 30, 2019 at 8:54

Mihai

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Comments

adiga · Accepted Answer · 2019-03-30 08:55:43Z

0

Its simple. Why complicating by reduce and etc.,

function convert(arr, key) {
  output = {};
  arr.forEach(function(item) {
    output[item[key]] = item;
  })
  console.log(output)
  return output
}

convert([{id: 1, value: 'abc'}, {id: 2, value: 'xyz'}], 'id')

https://jsfiddle.net/cvydtL7p/

edited Mar 30, 2019 at 8:55

adiga

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answered Mar 30, 2019 at 8:52

Alaksandar Jesus Gene

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1 Comment

adiga Over a year ago

How do I create a runnable Stack Snippet?

CertainPerformance · Accepted Answer · 2019-03-30 08:47:45Z

0

You're close, but you need nested bracket notation to get to the proper key name, eg

prev[current[v]]

or

a[item[keyName]] // as in code below

const convert = (arr, keyName) => arr.reduce((a, item) => {
  a[item[keyName]] = item;
  return a;
}, {});

console.log(
  convert([{id: 1, value: 'abc'}, {id: 2, value: 'xyz'}], 'id')
);

answered Mar 30, 2019 at 8:47

CertainPerformance

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Comments

baao · Accepted Answer · 2019-03-30 09:01:38Z

Your code is pretty much working, the only errors are to use bracket notation to access a variable key; for example:

obj[v] will evaluate to obj.id if v was id

The other error is that you are simply missing to return from your function, resulting in an undefined result

var arr = [{ id: 1, name: 'John', role: 'Developer'},
	   { id: 2, name: 'Jane', role: 'Lead'},
	   { id: 3, name: 'Robbie', role: 'QA'}];


function f(k, v) {
  //console.log(k);              
  return k.reduce((prev, current) => {
    prev[current[v]] = current;
    return prev;
  }, {})
}

console.log(f(arr, 'role'));

Also note that nothing after return will happen, so the console.log line in your reducer should be before that, otherwise it's ignored.

zb22 · Accepted Answer · 2019-03-30 09:32:12Z

0

You can use reduce and spread like this:

var arr = [{id: 1, value: 'abc'}, {id: 2, value: 'xyz'}];

const res = arr.reduce((total, curr) => {
  return {...total, [curr.id]: curr };
}, {});

console.log(res);

refs: reduce Spread syntax

answered Mar 30, 2019 at 9:32

zb22

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