Filter json by keys (not by value)

Question

I have this json:

json = [{
    "code3": "ALB",
    "asset": 9,
    "biodiversity": 4,
    "infrastructure": 15
}, {
    "code3": "GHN",
    "asset": 4,
    "biodiversity": 5,
    "infrastructure": 5,
}, {
    "code3": "TGO",
    "asset": 3,
    "biodiversity": 6,
    "infrastructure": 7
}]

I am trying to filtering it down to this in a for loop:

result = [{
    "code3": "ALB",
    "asset": 9
}, {
    "code3": "GHN",
    "asset": 4
}, {
    "code3": "TGO",
    "asset": 3
}]

What is the fastest way to do this. I know I could use json.forEach(j => del j["infrastructure"] ... or something similar but I am looking to filter out by the keys code3, asset instead

Check out this answer - https://stackoverflow.com/a/43106873/2570277 — Nick, Oct 02 '20 at 19:21
Does this answer your question? [how to map more than one property from array of object in javascript](https://stackoverflow.com/questions/53718887/how-to-map-more-than-one-property-from-array-of-object-in-javascript) — VLAZ, Oct 02 '20 at 19:21

score 2 · Answer 1 · answered Oct 02 '20 at 19:34

let json = [
     {
          "code3": "ALB",
          "asset": 9,
          "biodiversity": 4,
          "infrastructure": 15
     },
     {
          "code3": "GHN",
          "asset": 4,
          "biodiversity": 5,
          "infrastructure": 5,
      },
      {
           "code3": "TGO",
           "asset": 3,
           "biodiversity": 6,
           "infrastructure": 7
      }
];

let result = json.map(({code3, asset}) => ({code3, asset}));

console.log(result);

This might be confusing at first, so let's see how it works:

The .map method creates a new array with the output from the function on each element in the previous array.
- Example:

let nums = [0, 1, 2, 3];
let add1 = n => n + 1;

// The following two statements are equivalent:
nums = [add1(num[0]), add1(num[1]), add1(num[2]), add1(num[3])];
nums = nums.map(add1);

Object destructuring is the way that we get the input from the arrow function. It's a bit hard to explain, so perhaps this article will guide you through it:
- https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Destructuring_assignment
Lastly, we have object shorthand properties. This is how we return the result from the arrow function. If you have a variable with the same name as the property of an object and the same value as the value of that property, you can add it to the object without specifying the value.
- Example:

let a = 'foo', b = 42, c = {};
let o = {a, b, c}

// o = { a: 'foo', b: 42, c: {} }

Hopefully putting these parts together is intuitive by itself.

score 1 · Accepted Answer · answered Oct 02 '20 at 19:17

You can use .map:

let json = [
     {
          "code3": "ALB",
          "asset": 9,
          "biodiversity": 4,
          "infrastructure": 15
     },
     {
          "code3": "GHN",
          "asset": 4,
          "biodiversity": 5,
          "infrastructure": 5,
      },
      {
           "code3": "TGO",
           "asset": 3,
           "biodiversity": 6,
           "infrastructure": 7
      }
];

let list = json.map(e => {
     return {
          code3: e.code3,
          asset: e.asset
     }
});

console.log(list);

Even shorter as `.map(({code3, asset}) => ({code3, asset}))` — VLAZ, Oct 02 '20 at 19:19

Filter json by keys (not by value)

2 Answers2