How to map array of objects to key-values?

Question

In JS, I have an array A = [{k:"a",v:3},{k:"b",v:4}] consisting of objects, defining key-values. I want to generate array B:

let B = 
((A)=>{
    let B=[];
    for(let i of A)
        B[i.k]=i.v;
    return B;
})(A);

So that it maps A's object keys k to B's keys, and values v to its values. Is that achievable more easily, through Array mapreduce functions? Could you help me with correct syntax? SO that B (for our example) would be:

let B = [];
B["a"]=3;
B["b"]=4;
console.log( B );
[ a: 3, b: 4 ]

expected output is not clear. Can you please share expected output — brk
– brk, Commented Jul 22, 2019 at 16:10
expected output in this format [ a: 3, b: 4 ] is wrong,array cannot have value like this unless it is array of string. Are you looking for[{ a: 3},{ b: 4}] — brk
– brk, Commented Jul 22, 2019 at 16:13
If you are searching for a final structure that maps each key to the related value, forget about array. Instead use a Map or an object. — Shidersz
– Shidersz, Commented Jul 22, 2019 at 16:15
@brk Sorry I dont know how is this called, but this result should be possible produce on node.js and in browser console, despite of naming scheme. Result is simple, please dont dig too deep. Just how to rewrite code with mapreduce? — xakepp35
– xakepp35, Commented Jul 22, 2019 at 16:17

Bergi · Accepted Answer · 2019-07-22 16:20:00Z

1

You can drop the IIFE and use

const B = {};
for (const {k, v} of A)
    B[k] = v;

A reduce solution is also possible, but less concise:

const B = A.reduce((acc, {k, v}) => {
    acc[k] = v;
    return acc;
}, {});

answered Jul 22, 2019 at 16:20

Bergi

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1 Comment

xakepp35 Over a year ago

Thank you, I would not abuse arrays. Just wanted to see possible implementation with reduce! (I knew its possible just forgot how)

Nina Scholz · Accepted Answer · 2019-07-22 16:26:19Z

1

You could take Object.fromEntries with mapped arrays for a key/value pair.

var array = [{ k: "a", v: 3 }, { k: "b", v: 4 }],
    object = Object.fromEntries(array.map(({ k, v }) => [k, v]));

console.log(object);

answered Jul 22, 2019 at 16:26

Nina Scholz

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1 Comment

xakepp35 Over a year ago

Also nice approach! Thanks for your input.

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