Swap array keys with inner object value

Question

I have this array which holds objects;

let arr = [
    {
        "id": 1,
        "level": "2",
    },
    {
        "id": 2,
        "level": "3",
    }
]

By default the array has keys starting from 0 and it looks like this:

[
    0: {id: 1, level:2},
    1: {id: 2, level:3}
]

How can I transform it so that the keys are the values of the property 'level'? It should look like this:

[
    2: {id:1, level:2},
    3: {id:1, level:3}
]

So far I have tried this but it doesn't remove the original keys:

arr.map((v, k) => ({[v.level]: v}));

So I have something like this:

[
    0: {2:
        {id: 1, level:2}
    },
    1: {3:
        {id: 2, level:3}
    }
]

arr.map((v, k) => ({[v.level]: v})); your code should give the result — Rajdeep D
– Rajdeep D, Commented Jun 9, 2021 at 10:41
The result you're expecting is impossible, you need an object, not an array. { 2: { id: 1, level: 2 }, 3: {id: 2, level: 3 } } — ZeroBased_IX
– ZeroBased_IX, Commented Jun 9, 2021 at 10:47
@Petyor put it in snippet in the question, you will see your expected result. — Rajdeep D
– Rajdeep D, Commented Jun 9, 2021 at 10:49

lvendrame · Accepted Answer · 2021-06-09 10:45:57Z

1

You need to populate a new array using reduce:

arr.reduce((prev, curr) => { prev[curr.level] = curr; return prev }, [])

answered Jun 9, 2021 at 10:45

lvendrame

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Comments

spender · Accepted Answer · 2021-06-09 11:02:16Z

0

I think I prefer the reduce method, but you could also construct an "array-like" (i.e. an object with numeric keys and a length property) and pass it to Array.from

const maxIdx = Math.max(...arr.map(v => parseInt(v.level, 10)))
const arrLen = maxIdx + 1;
const arrayLike = { 
    ...Object.fromEntries(arr.map(v => [v.level, v])), 
    length: arrLen
};
const mappedArray = Array.from(arrayLike);

For output of

[undefined, undefined, {
  "id": 1,
  "level": "2"
}, {
  "id": 2,
  "level": "3"
}]

edited Jun 9, 2021 at 11:02

answered Jun 9, 2021 at 10:52

spender

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