Create an array of attributes from a list of objects

Question

What I'm trying to do is read this array of objects below and from there build a list with the free values.

const data = [
  {
      "house01": {
        "free": 6
      },
      "house02": {
        "free": 2
      },
      "house03": {
        "free": 1
      },
  }
]


console.log(data.map((item) => item.free))

Response

[undefined]

Expected response

[6, 2, 1]

What I don't understand is why the result doesn't go as expected.

Why is the data structured like that? An array of objects with one object with consecutive numbers as keys. Why nit something like const data = { houses: [{ "free": 6 }, { "free": 2 }] } with an additional houseId property in each house object, if required — adiga
– adiga, Commented Apr 30, 2021 at 8:22

Nina Scholz · Accepted Answer · 2021-04-30 08:35:18Z

5

You need two iterations, one for the array and another for the object's values to get the wanted property.

const data = [{ house01: { free: 6 }, house02: { free: 2 }, house03: { free: 1 } }];

console.log(data.flatMap(item => Object.values(item).map(({ free }) => free)));

By having unwanted keys, you need to add a filtering and take the entries to get the key as well.

const
    data = [{ house01: { free: 6 }, house02: { free: 2 }, house03: { free: 1 }, dontcountthisdata: "USA" }],
    unwanted = ['dontcountthisdata'];

console.log(data.flatMap(item => Object
    .entries(item)
    .filter(([key]) => !unwanted.includes(key))
    .map(([, { free }]) => free)
));

edited Apr 30, 2021 at 8:35

answered Apr 30, 2021 at 8:18

Nina Scholz

388k26 gold badges367 silver badges417 bronze badges

Sign up to request clarification or add additional context in comments.

5 Comments

RoktSe Over a year ago

What if I have an object that I don't want to be counted in this flatmap ()? Something like that: [ { "house01": { "free": 6 }, "house02": { "free": 2 }, "house03": { "free": 1 }, "dontcountthisdata": "USA", } ]

Nina Scholz Over a year ago

do you have only one or more unwanted properties?

RoktSe Over a year ago

More than one unwanted properties

RoktSe Over a year ago

Thank you so much! Quick question, do you know any functions that return data in the order they appear in the list? When I use this function that you created they appear in a different order from the parent list, for example the right would be [6, 2,1] but something like [2, 6, 1] appears

Nina Scholz Over a year ago

the keys of an object are usually sorted by index like numbers sorted, first, then strings/other numbers in insertation order and at last symbols in insertation order.

Collectives™ on Stack Overflow

Create an array of attributes from a list of objects

1 Answer 1

5 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

5 Comments

Your Answer

Sign up or log in

Post as a guest

Related