How to get all the keys of objects in an array in JavaScript

Question

I am wondering what is a better approach to extract all the keys and values of objects in an array as separate arrays. My approach requires me to flatten the array after extracting keys and values of the object by mapping over the array.

Input

const input = [{"a": 1, "b": 2}, {"c": 3}, {"d": 4}, {}, {"e": null, "f": 6, "g": 7}];

Output

const keys = ["a", "b", "c", "d", "e", "f", "g"];

const values = [1, 2, 3, 4, null, 6, 7];

My Solution

const input = [{
  "a": 1,
  "b": 2
}, {
  "c": 3
}, {
  "d": 4
}, {}, {
  "e": null,
  "f": 6,
  "g": 7
}];
const keys = input.map(obj => [].concat(Object.keys(obj))).flat();
console.log(keys);
const values = input.map(obj => [].concat(Object.values(obj))).flat();
console.log(values);

This would be a question for CodeReview

trincot
– trincot

2019-11-28 09:08:12 +00:00
Commented Nov 28, 2019 at 9:08 — trincot
– trincot, Commented Nov 28, 2019 at 9:08
Aah, thanks for introducing me to this wonderful platform.

sibasishm
– sibasishm

2019-11-28 09:09:47 +00:00
Commented Nov 28, 2019 at 9:09 — sibasishm
– sibasishm, Commented Nov 28, 2019 at 9:09

mplungjan · Accepted Answer · 2019-11-28 09:10:38Z

4

You can use the flatMap which is what you have implemented

The flatMap() method first maps each element using a mapping function, then flattens the result into a new array. It is identical to a map() followed by a flat() of depth 1, but flatMap() is often quite useful, as merging both into one method is slightly more efficient.

const input = [{
  "a": 1,
  "b": 2
}, {
  "c": 3
}, {
  "d": 4
}, {}, {
  "e": null,
  "f": 6,
  "g": 7
}];

const keys = input.flatMap(Object.keys);
const values = input.flatMap(Object.values);

console.log(keys,values)

edited Nov 28, 2019 at 9:10

answered Nov 28, 2019 at 9:08

mplungjan

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1 Comment

trincot Over a year ago

There is no need to create a new callback function. You can just do flatMap(Object.keys)... etc.

mplungjan · Accepted Answer · 2019-11-28 09:12:10Z

1

Try one reduce function so you don't do two loops, and get it all done in one loop?

const input = [{
  "a": 1,
  "b": 2
}, {
  "c": 3
}, {
  "d": 4
}, {}, {
  "e": null,
  "f": 6,
  "g": 7
}];

const { keys, values } = input.reduce((accum, obj) => ({
  keys: [...accum.keys, ...Object.keys(obj)],
  values: [...accum.values, ...Object.values(obj)],
}), { keys: [], values: [] });

console.log(keys, values)

edited Nov 28, 2019 at 9:12

mplungjan

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answered Nov 28, 2019 at 9:08

Kousha

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Comments

StepUp · Accepted Answer · 2019-11-28 09:13:41Z

0

You can get key and then flat an array:

const input = [
  { "a": 1, "b": 2 },
  { "c": 3 }, { "d": 4 },
  {},
  { "e": null, "f": 6, "g": 7 }
];

const keys = input.map(a=> Object.keys(a)).flat();
const values = input.map(a=> Object.values(a)).flat();

console.log(keys)
console.log(values)

answered Nov 28, 2019 at 9:13

StepUp

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