How to map get values by dynamic key from array of object?

Question

I want to fetch object values by dynamic key inside map() if possible.

const array = [
  { "ts": 1620988054, "KEY1": 14, "KEY2": 23, "KEY3": 58 },
  { "ts": 1620901654, "KEY1": 46, "KEY2": 34, "KEY3": 42 },
  { "ts": 1620898054, "KEY1": 16, "KEY2": 44, "KEY3": 24 }
];
let data = {};
const arrayOfKeys = [ "KEY1", "KEY2", "KEY3" ];
const keyObject = { "KEY1": "KEY1", "KEY2": "KEY2", "KEY3": "KEY3" };

for (let index = 0; index < arrayOfKeys.length; index++) {
  const key = Object.keys(keyObject)[index];
  data[key] = array.map(({ KEY1 }) => KEY1);
  data[key] = array.map(({ KEY2 }) => KEY2);
  data[key] = array.map(({ KEY3 }) => KEY3);
}

console.log(data);

bel3atar · Accepted Answer · 2021-05-14 12:22:36Z

1

const array = [
      {"ts":1620988054, "KEY1":14, "KEY2":23, "KEY3":58},
      {"ts":1620901654, "KEY1":46, "KEY2":34, "KEY3":42},
      {"ts":1620898054, "KEY1":16, "KEY2":44, "KEY3":24}];
    
    const data = array.reduce((acc, cur) => { // loop through array
       const {ts, ...rest} = cur; // for each item, isolate ts from the rest
       Object.entries(rest).forEach(([k, v]) => { // loop through the rest
        if (k in acc) acc[k].push(v) // if we already have an array for the key, push the new value to it
        else acc[k] = [v]; // else create a new array with that key/value pair
       });
       return acc
    }, {});
  
    
    
    console.log(data);

edited May 14, 2021 at 12:22

answered May 14, 2021 at 12:06

bel3atar

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3 Comments

Dev M Over a year ago

I didn't understand it very well but ty anyway.

bel3atar Over a year ago

Basically I loop through each item of the array, I then isolate ts and put all of the other keys and values in the rest variable. I then loop through rest and put the values in the array corresponding to the key.

bel3atar Over a year ago

@DevM I've added comments. This solution is dynamic and allows you not to hard-code an array of keys

Mr. Polywhirl · Accepted Answer · 2021-05-14 12:13:38Z

If you want an object containing keys that correlate with your array of keys, you can reduce the items in the array by reducing over the array, and within the items, reducing the keys.

const array = [
  { "ts": 1620988054, "KEY1": 14, "KEY2": 23, "KEY3": 58 },
  { "ts": 1620901654, "KEY1": 46, "KEY2": 34, "KEY3": 42 },
  { "ts": 1620898054, "KEY1": 16, "KEY2": 44, "KEY3": 24 }
];
const arrayOfKeys = [ "KEY1", "KEY2", "KEY3" ];

const data = array.reduce(
  (accOuter, record) => arrayOfKeys
    .reduce((accInner, key) => ({
      ...accInner,
      [key]: record[key]
        ? [...accInner[key], record[key]]
        : accInner[key]
    }),
  accOuter),
  Object.fromEntries(arrayOfKeys.map(key => [ key, [] ])));

console.log(data);

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