loop multiple arrays and sum the values of same keys

Question

I have multiples arrays for different length , Each array has objects of key ,value pairs .

[{date: "2018-11-26", totalHours: 2},{date: "2018-11-27", totalHours: 2}]
[{date: "2018-11-26", totalHours: 4},{date: "2018-11-27", totalHours: 2},{date: "2018-11-28", totalHours: 8}]
[{date: "2018-11-26", totalHours: 4},{date: "2018-11-27", totalHours: 2},{date: "2018-11-28", totalHours: 6},{date: "2018-11-30", totalHours: 9}]

How to sum the totalHours of same dates considering all arrays?

Concat all arrays into one and then [group by](https://stackoverflow.com/a/53516535/1641941) the date key. — HMR, Nov 29 '18 at 11:10

score 0 · Answer 1 · edited Nov 29 '18 at 11:11

0

You can use the reduce function as follows:

const x = [{ date: '2018-11-26', totalHours: 2 }, { date: '2018-11-27', totalHours: 2 }]

const sum = x.reduce((a, c) => a + c.totalHours, 0)
console.log(sum) // 4

edited Nov 29 '18 at 11:11

Jonas Wilms

132,000
20
149
151

answered Nov 29 '18 at 11:09

ninesalt

4,054
5
35
75

if you would add a third entry, `a` is a number at the second iteration and `a.totalHours` would fail then – Jonas Wilms Nov 29 '18 at 11:12
@jonaswilms Yeah, your edit fixes that – ninesalt Nov 29 '18 at 11:13

score 0 · Answer 2 · answered Nov 29 '18 at 11:10

You could first create one array with spread syntax and then use reduce method to calculate sum.

let a = [{date: "2018-11-26", totalHours: 2},{date: "2018-11-27", totalHours: 2}]
let b = [{date: "2018-11-26", totalHours: 4},{date: "2018-11-27", totalHours: 2},{date: "2018-11-28", totalHours: 8}]
let c = [{date: "2018-11-26", totalHours: 4},{date: "2018-11-27", totalHours: 2},{date: "2018-11-28", totalHours: 6},{date: "2018-11-30", totalHours: 9}]

let sum = [...a, ...b, ...c].reduce((r, {date, totalHours}) => {
  if(!r[date]) r[date] = totalHours;
  else r[date] += totalHours;
  return r;
}, {})

console.log(sum)

score 0 · Answer 3 · answered Nov 29 '18 at 11:23

let a = [
    ...[{date: "2018-11-26", totalHours: 2},{date: "2018-11-27", totalHours: 2}],
    ...[{date: "2018-11-26", totalHours: 4},{date: "2018-11-27", totalHours: 2},{date: "2018-11-28", totalHours: 8}],
    ...[{date: "2018-11-26", totalHours: 4},{date: "2018-11-27", totalHours: 2},{date: "2018-11-28", totalHours: 6},{date: "2018-11-30", totalHours: 9}]
];

let result = {};

a.forEach((i) => {
  result[i.date] = result[i.date] || { date: i.date, totalHours: 0 };
  result[i.date].totalHours += i.totalHours;
});

result = Object.values(result)
console.log(result);

loop multiple arrays and sum the values of same keys

3 Answers3

Linked