Convert an array of arrays to an array of objects with mapped properties

Question

What is the best way of converting an array of arrays to objects so that the indices are replaced with given mapping properties.

For example:

let cars = [
    [1, "Honda", "Honda description here"],
    [2, "Mercedes", "Mercedes description here"],
    [3, "Toyota", "Toyota description here"],
];

let mapping = {
    0: 'id',
    1: 'name',
    2: 'description',
};

So the final result is:

[
    {id: 1, name: 'Honda', description: 'Honda description here'},
    {id: 2, name: 'Mercedes', description: 'Mercedes description here'},
    {id: 3, name: 'Toyota', description: 'Toyota description here'},
];

The outer loop is over the cars, the inner loop is over the mappings. The inner loop adds properties to the object, the outer loop pushes the properties onto the result array. You can use the .map() function for the outer loop. — Barmar
– Barmar, Commented Oct 2, 2019 at 21:38

Bibberty · Accepted Answer · 2019-10-02 21:45:28Z

1

Use a map command. Note: this code assumes there are mappings for each element of the array.

let cars = [
    [1, "Honda", "Honda description here"],
    [2, "Mercedes", "Mercedes description here"],
    [3, "Toyota", "Toyota description here"],
];

let mapping = {
    0: 'id',
    1: 'name',
    2: 'description',
};

let result = cars.map(a => {
  let obj = {};
  a.forEach((v,i) => {
    obj[mapping[i]] = v;
  });
  return obj;
});

console.log(result);

answered Oct 2, 2019 at 21:45

Bibberty

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M0nst3R · Accepted Answer · 2019-10-02 21:59:45Z

1

You can achieve the merged result by using a combination of:

[].map() on the cars array to loop through its elements.
[].reduce() on each car element to reduce the three value into one object, taking advantage of the ordering you have in the mapping object.

Here is a solution that can be shortened into a one-liner:

let cars = [
    [1, "Honda", "Honda description here"],
    [2, "Mercedes", "Mercedes description here"],
    [3, "Toyota", "Toyota description here"],
];
let mapping = {
    0: 'id',
    1: 'name',
    2: 'description',
};
let result = cars.map((car) => (
    car.reduce((acc, cur, i) => (
        Object.assign(acc, { [mapping[i]]: cur })
    ), {})
));

console.log(result);

answered Oct 2, 2019 at 21:59

M0nst3R

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3 Comments

James Over a year ago

acc[mapping[i]] = cur; return acc; is uglier but avoids creating a new object in order to copy each property.

M0nst3R Over a year ago

Incorrect, Object.assign(acc, { [mapping[i]]: cur }) does not create a new object, Object.assign({}, acc, { [mapping[i]]: cur }) does.

James Over a year ago

Right you are! Cheers.

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