is it possible to use .map() to create an object from an array of objects?

Question

Here is a representative sample of data from a larger dataset in a project:

const data = [
                { scenario: '328', buckets: 2 },
                { scenario: '746', buckets: 1 },
                { scenario: '465', buckets: 2 }
            ];

There is a need to reformat the data into an object with the scenario value as the key and the bucket value as the value, like this:

I have been able to achieve this outcome by using .forEach like so:

const reformattedData = {};
            data.forEach(o => {
                reformattedData[o.scenario] = o.buckets;
            });

but I suspect there is a more concise way to accomplish the same output. I have tried .map as follows

const reformattedData = data.map(o => ({ [o.scenario] : o.buckets}));

but it doesn't give the intended output. Instead it gives [{328: 2}, {746: 1}, {465: 2}]. What needs to be modified in the .map() version to attain the desired output?

I advise against using `.map()` for trivial iteration. At best, you can create an array of key-value pairs and then use `Object.fromEntries()` (you can [use a generator](https://stackoverflow.com/a/64401229/) to map into key-value pairs to feed into `fromEntries` if you want) but a `.forEach()` (or a normal loop) is more straight forward. You can also `.reduce()` into an object. — VLAZ, Dec 09 '20 at 17:37

score 1 · Answer 1 · answered Dec 09 '20 at 17:33

1

You can use reduce()

const data = [
   { scenario: '328', buckets: 2 },
   { scenario: '746', buckets: 1 },
   { scenario: '465', buckets: 2 }
];
const res = data.reduce((ac, {scenario:s, buckets:b}) => ({...ac, [s]:b}), {});
console.log(res)

answered Dec 09 '20 at 17:33

Maheer Ali

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Nina Scholz · Accepted Answer · 2020-12-09T17:38:52.743

You could map the data and create an object from the entries with Object.fromEntries.

const
    data = [{ scenario: '328', buckets: 2 }, { scenario: '746', buckets: 1 }, { scenario: '465', buckets: 2 }],
    result = Object.fromEntries(data.map(({ scenario, buckets }) =>
        [scenario, buckets]
    ));

console.log(result);

Another solution by spreading objects for Object.assign.

const
    data = [{ scenario: '328', buckets: 2 }, { scenario: '746', buckets: 1 }, { scenario: '465', buckets: 2 }],
    result = Object.assign(
        {},
        ...data.map(({ scenario, buckets }) => ({ [scenario]: buckets }))
    );

console.log(result);

Was just going to add this as second solution. – Maheer Ali Dec 09 '20 at 17:36 — Maheer Ali, Dec 09 '20 at 17:36

is it possible to use .map() to create an object from an array of objects?

2 Answers2