How to convert Object with nested arrays to array of flat objects? [duplicate]

Question

I have object with array of options. On each option I need to create flat object. Like so

name: 'win10',
        architectures: ['x64', 'x86'],
        languages: ['en', 'ru'],

Transforms into:

[
{ name: 'win10',
        architectures 'x64',
        languages: 'en',
}, {
name: 'win10',
        architectures:  'x86',
        languages: 'ru',
}, {
name: 'win10',
        architectures: 'x64',
        languages: 'en',
}, {
name: 'win10',
        architectures: 'x86',
        languages: 'ru',
}
]

user15770830 · Accepted Answer · 2021-04-27 11:08:21Z

1

This should do:


let input = {
        name: 'win10',
        architectures: ['x64', 'x86'],
        languages: ['en', 'ru']
};

function flatten(system) {
        let output = [];

        for (let i = 0; i < system.architectures.length; i++) {
                const arch = system.architectures[i];
                for (let j = 0; j < system.languages.length; j++) {
                        const lang = system.languages[j];
                        output = [...output, {
                                name: system.name,
                                architectures: arch,
                                language: lang
                        }];
                }
        }
        return output;
}

const output = flatten(input);

console.log(output);

answered Apr 27, 2021 at 11:08

user15770830

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4 Comments

adiga Over a year ago

Is there any reason to create a new array in every loop with output = [...output, {..}] instead of simply doing output.push()?

user15770830 Over a year ago

Both approaches are valid, output = [...output, {..}] unpacks the output array and appends the object to it. You can choose .push() if you prefer it

adiga Over a year ago

But a new array is being created in every iteration and another array is being spread for no reason. It makes sense doing something like react where mutating the array isn't allowed. If it is being assigned back to the ouptut variable, this is completely pointless

user15770830 Over a year ago

As I've said, you can choose any of them. It's up to you :)

Tony Tom · Accepted Answer · 2021-04-27 11:16:35Z

1

This is another approach

var x = { name: 'win10',
        architectures: ['x64', 'x86'],
        languages: ['en', 'ru'] }
var k = [];
 x.architectures.forEach(p => {
 x.languages.forEach((y => {
    k.push({name: x.name, architectures:p,languages:y})
  }))
})

console.log(k)

answered Apr 27, 2021 at 11:16

Tony Tom

1,5831 gold badge12 silver badges19 bronze badges

5 Comments

user15770830 Over a year ago

This is almost the same as my approach but you must note that forEach is waaaay slower than for() {...}

Tony Tom Over a year ago

It depends on the array size, always go with the latest syntax

user15770830 Over a year ago

It's not as important in this example but when going for performance, you should keep that in mind, the speedup is 150-200% (from my tests)

Tony Tom Over a year ago

I agree for loop is much faster than forEach but syntax wise forEach is cleaner more readability and chances of accidental errors are less If you are interested to know more about forEach and for you can check this doc alligator.io/js/foreach-vs-for-loops

user15770830 Over a year ago

And I agree forEach is quite a bit cleaner. Thanks for the great document on the differences!

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