javascript sum array of arrays of objects together

Question

i have an array with the following format

[
[{year:2015, value:23000, value1:1000},{year:2016,value:1000, value1:2000},{year:2017,value:400, value1:3000}],
[{year:2015, value:10000, value1:1000},{year:2016,value:2000, value1:3000},{year:2017,value:500, value1:2000}],
]

i want to sum them together, in this example, i want to have

[{year:2015,value:33000, value1:2000},{year:2016,value:3000, value1:5000},{year:2017,value:900, value1:5000}]

if there are only two arrays in the array but there maybe more arrays in the bigger array. how can i achieve this? currently, i am not able to figure out a good method. Thanks

Are there only two only two levels of arrays, or can inner arrays have arrays in them as well? — yogur
– yogur, Commented Apr 29, 2017 at 13:47

RomanPerekhrest · Accepted Answer · 2017-04-29 14:12:44Z

2

Ecmascript5 solution:

var arr = [
        [{year:2015, value:23000, value1:1000},{year:2016,value:1000, value1:2000},{year:2017,value:400, value1:3000}],
        [{year:2015, value:10000, value1:1000},{year:2016,value:2000, value1:3000},{year:2017,value:500, value1:2000}]
    ],
    
    // summing up values for each `year`
    years = arr.reduce(function (r, a) {
        a.forEach(function (o) {
            y = o.year;
            if (Array.isArray(r[y])) {
                r[y][0] += o.value;
                r[y][1] += o.value1;
            } else {
                r[y] = [o.value, o.value1];
            }
        });
        return r;
    }, {}),

    // constructing the resulting array containing objects with `year` totals
    result = Object.keys(years).map(function (y) {
        return {year: y, value: years[y][0], value1: years[y][1]};
    });

console.log(result);

edited Apr 29, 2017 at 14:12

answered Apr 29, 2017 at 13:53

RomanPerekhrest

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4 Comments

onegun Over a year ago

actually, there are more properties inside the objects, i tested in that case, this solution failed to work.[{year:2015, value:23000, value1:1000},{year:2016,value:1000, value:200},{year:2017,value:400, value1:600}],

RomanPerekhrest Over a year ago

@onegun, you didn't mention that in your question and you didn't post the extended input array

onegun Over a year ago

yes, i was looking for a general solution, thought that cause the confusion, i will edit that

RomanPerekhrest Over a year ago

@onegun, even though you have changed your initial condition, I've updated my answer. See the update

Zohaib Ijaz · Accepted Answer · 2017-04-29 14:00:32Z

1

You can loop over the items and add value agains a year number (key) in a map / object.

var data = [
[{year:2015, value:23000},{year:2016,value:1000},{year:2017,value:400}],
[{year:2015, value:10000},{year:2016,value:2000},{year:2017,value:500}],
];

var output = {};

data.forEach(function(item) {
  item.forEach(function(obj) {
    output[obj.year] = (output[obj.year] || 0) + obj.value;
  });
});
output = [output]

console.log(output);

One way is to flat this 2D array first.

var output = {};
var flatArray = data.reduce(function(a, b) {
  return a.concat(b);
}, []);

flatArray.forEach(function(obj) {
  output[obj.year] = (output[obj.year] || 0) + obj.value;
});

output = [output]
console.log(output);

output: [{ 2015: 33000, 2016: 3000, 2017: 900 }]

edited Apr 29, 2017 at 14:00

answered Apr 29, 2017 at 13:52

Zohaib Ijaz

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5 Comments

ThisClark Over a year ago

Your output doesn't match his: [{year:2015,value:33000},{year:2016,value:3000},{year:2017,value:900}] where his is an array of objects and yours is an array of one object.

Zohaib Ijaz Over a year ago

@ThisClark outer array does not make sense but I've update my code to match the exact same output.

onegun Over a year ago

actually, there are more properties inside the objects, i tested in that case, this solution failed to work.[{year:2015, value:23000, value1:1000},{year:2016,value:1000, value:200},{year:2017,value:400, value1:600}], that is why i want that kind of output

Zohaib Ijaz Over a year ago

@onegun An object can't have two keys with same name. {year:2016,value:1000, value:200} . Also you did not mentioned this in your question

onegun Over a year ago

hi i have updated the question, they are not same name properties, but one is value another is value1 used in the example

Nina Scholz · Accepted Answer · 2017-04-29 17:39:04Z

You could use a hash table for collecting a single year and a nested approach for the arrays with iterating all properties of the given objects.

Then create new properties and add the actual value.

It works with an arbitrary count of properties.

var data = [[{ year: 2015, value: 23000, value1: 1000 }, { year: 2016, value: 1000, value1: 2000 }, { year: 2017, value: 400, value1: 3000 }], [{ year: 2015, value: 10000, value1: 1000 }, { year: 2016, value: 2000, value1: 3000 }, { year: 2017, value: 500, value1: 2000 }]],
    result = data.reduce(function (hash) {
        return function (r, a) {
            a.forEach(function (o) {
                if (!hash[o.year]) {
                    hash[o.year] = { year: o.year };
                    r.push(hash[o.year]);
                }
                Object.keys(o).forEach(function (k) {
                    if (k !== 'year') {
                        hash[o.year][k] = (hash[o.year][k] || 0) + o[k];
                    }
                });
            });
            return r;
        };
    }(Object.create(null)), []);

console.log(result);

.as-console-wrapper { max-height: 100% !important; top: 0; }

HenryDev · Accepted Answer · 2017-04-29 15:29:36Z

Here's a working solution. This will do what you're looking for. Hope it helps!

var arr =   [
      [{year:2015, value:23000, value1:1000},{year:2016,value:1000, value1:2000},{year:2017,value:400, value1:3000}],
          [{year:2015, value:10000, value1:1000},{year:2016,value:2000, value1:3000},{year:2017,value:500, value1:2000}],
      ]

var result = [];

  for(var i = 0; i < arr[0].length; i++){
      var count = 0
      var count2 = 0;
      for(var j = 0; j < arr.length; j++){
       var year = arr[j][i].year;
       count  += arr[j][i].value;
       count2 += arr[j][i].value1;
      }
      result.push({
          year: year,
          value: count,
          value1: count2
      });
  }
  console.log(result);

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