Flatten nested array key value pairs without specifying each key in Javascript

Question

Given an array like this:

[
    { force_x: [1, 2, 3], force_y: [0.3, 0.4, 0.5] },
    { force_x: [4, 5, 6], force_y: [0.0, 0.0, 0.0] },
    { motion_x: [0.7, 0.7, 0.7] }
]

How could I use Javascript to reduce this to an array like this without specifying any keys:

[
    { force_x: 1, force_y: 0.3 },
    { force_x: 2, force_y: 0.4 },
    { force_x: 3, force_y: 0.5 },
    { force_x: 4, force_y: 0.0 },
    { force_x: 5, force_y: 0.0 },
    { force_x: 6, force_y: 0.0 },
    { motion_x: 0.7 },
    { motion_x: 0.7 },
    { motion_x: 0.7 }
 ]

This answer could work but I don't want to specify the key name, I want it to do it for every keys automatically.

const output = input.flatMap(o => 
    o.emailAddresses.map(e => ({force_x: e }) )
)

Unmitigated · Accepted Answer · 2022-09-30 14:07:44Z

2

You can use Object.entries to get all the key value pairs and work with that.

let arr=[{force_x:[1,2,3],force_y:[.3,.4,.5]},{force_x:[4,5,6],force_y:[0,0,0]},{motion_x:[.7,.7,.7]}];
let res = arr.flatMap(x => {
  const entries = Object.entries(x);
  return entries[0][1].map((_, i) => Object.fromEntries(
    entries.map(([k, v]) => [k, v[i]])));
});
console.log(res);

answered Sep 30, 2022 at 14:07

Unmitigated

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2 Comments

Captain Yoshi Over a year ago

Nice! Thank you very much. Coming from c++ land, so this is all black magic to me :)

vsync Over a year ago

this works well as long as the number of items per array is the same for all keys. A preferred solution would not create keys for non-existing array items. For example, change force_x:[1,2,3] to force_x:[1]

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