Iterate over an object array in JS

Question

I have the following object:

obj = [
    { 1: 20, 2: 26, 3: 14},
    { 1: 12, 2: 25, 3: 15},
    { 1: 14, 2: 13, 3: 19},
    { 1: 16, 2: 32, 3: 21}
]

and I want to multiply by 2 each of the positions and then add them to each position, let me explain: I multiply each value by 2 and this is the partial result:

obj = [
    { 1: 40, 2: 52, 3: 28},
    { 1: 24, 2: 50, 3: 30},
    { 1: 28, 2: 26, 3: 38},
    { 1: 32, 2: 72, 3: 42}
]

then I must add each key and add the total by adding a new array at the end inside the initial object, and this should be the final result:

obj = [
    { 1: 20, 2: 26, 3: 14},
    { 1: 12, 2: 25, 3: 15},
    { 1: 14, 2: 13, 3: 19},
    { 1: 16, 2: 32, 3: 21},
    { 1: 104, 2: 200, 3: 138}
]

A lot of the math you have given in the example is currently wrong. 32 * 2 is not 72, 40 + 24 + 28 + 32 is not 104 -- it's 124 — Samathingamajig
– Samathingamajig, Commented Nov 10, 2020 at 4:07

kapil pandey · Accepted Answer · 2020-11-10 04:15:10Z

5

Iterate over each array object(row) using map.
Then for each key in that row multiply it by 2 using reduce and in the end return that row (containing result of 2's multiply)
While multiplying each row by 2 we also calculate the sum of key*2 for each row.
Push sumRow to the original object

let obj = [
  { 1: 20, 2: 26, 3: 14},
  { 1: 12, 2: 25, 3: 15},
  { 1: 14, 2: 13, 3: 19},
  { 1: 16, 2: 32, 3: 21}
]
let sumRow = {}
let partialRes = obj.map(row => Object.keys(row).reduce((acc, key) => {
  acc[key] = row[key] * 2
  sumRow[key] = sumRow[key] ? sumRow[key] + acc[key] : acc[key]
  return acc
}, {}))

obj.push(sumRow)
console.log(obj)

edited Nov 10, 2020 at 4:15

answered Nov 10, 2020 at 4:08

kapil pandey

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Comments

Derek Wang · Accepted Answer · 2020-11-10 04:02:40Z

2

Using Object.keys, you can get all key of the object and using Array.prototype.forEach, you can loop the keys and do the operation as follows.

const input = [
  { 1: 20, 2: 26, 3: 14},
  { 1: 12, 2: 25, 3: 15},
  { 1: 14, 2: 13, 3: 19},
  { 1: 16, 2: 32, 3: 21}
];

const sumObj = {};
input.forEach((item) => {
  Object.keys(item).forEach((key) => {
    item[key] *= 2;
    sumObj[key] ? sumObj[key] += item[key] : sumObj[key] = item[key];
  });
});

input.push(sumObj);
console.log(input);

answered Nov 10, 2020 at 4:02

Derek Wang

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Comments

Samathingamajig · Accepted Answer · 2020-11-10 04:06:52Z

2

You can use Array.prototype.reduce() and push the result from that into the original array (or add it another way)

obj = [
  { 1: 20, 2: 26, 3: 14},
  { 1: 12, 2: 25, 3: 15},
  { 1: 14, 2: 13, 3: 19},
  { 1: 16, 2: 32, 3: 21}
]

console.log(obj);

obj.push(obj.reduce((acc, val) => ({
  1: acc[1] + val[1] * 2,
  2: acc[2] + val[2] * 2,
  3: acc[3] + val[3] * 2
}), {1: 0, 2: 0, 3: 0}));

console.log(obj);

answered Nov 10, 2020 at 4:06

Samathingamajig

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