Sum object array of varying length by value

Question

What is the best way to sum an object array of varying length that looks like this:

data = [{"category":"category1","months":{"1":34,"2":67,"3":29,...}
{"category":"category2","months":{"1":34,"2":627,"3":292,...}
{"category":"category3","months":{"1":46,"2":665,"3":129,...}
{"category":"category4","months":{"1":624,"2":667,"3":629,...}
{"category":"category5","months":{"1":32,"2":637,"3":299,...}
}]

I want to basically group by month and sum and assign that to a total category. So I would get a new object that looks like the following that I would push to my data object:

{"category":"total","months":{"1":770,"2":2663,"3":1378,...}

I would end up with:

data = [{"category":"category1","months":{"1":34,"2":67,"3":29,...}
{"category":"category2","months":{"1":34,"2":627,"3":292,...}
{"category":"category3","months":{"1":46,"2":665,"3":129,...}
{"category":"category4","months":{"1":624,"2":667,"3":629,...}
{"category":"category5","months":{"1":32,"2":637,"3":299,...}
{"category":"total","months":{"1":770,"2":2663,"3":1378,...}
}]

Yasin Yaqoobi · Accepted Answer · 2016-12-13 01:56:06Z

1

let data = [
{"category":"category1","months":{"1":34,"2":67,"3":29}},
{"category":"category2","months":{"1":34,"2":627,"3":292}},
{"category":"category3","months":{"1":46,"2":665,"3":129}},
{"category":"category4","months":{"1":624,"2":667,"3":629}},
{"category":"category5","months":{"1":32,"2":637,"3":299}},
];

let total = {"category":"total","months":{}};

data.forEach(category => {
      for(let prop in category.months){
          if (total.months[prop]){
            total.months[prop] += category.months[prop];
          }
          else{
            total.months[prop] = category.months[prop];
          }
      }
});

data.push(total);

edited Dec 13, 2016 at 1:56

answered Dec 12, 2016 at 2:24

Yasin Yaqoobi

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Comments

kukkuz · Accepted Answer · 2016-12-12 02:15:50Z

Use Array.prototype.reduce and a hash table to get the 'total' object and later on push it back to the data to obtain the data structure that you want.

See demo below:

var data=[{"category":"category1","months":{"1":34,"2":67,"3":29}},{"category":"category2","months":{"1":34,"2":627,"3":292}},{"category":"category3","months":{"1":46,"2":665,"3":129}},{"category":"category4","months":{"1":624,"2":667,"3":629}},{"category":"category5","months":{"1":32,"2":637,"3":299}}]

var result = data.reduce(function(hash){
  return function(p,c){
    Object.keys(c.months).forEach(function(e){
      if(e in p.months) {
        p.months[e] += c.months[e];
      } else {
        p.months[e] = +c.months[e];
      }
    });
    return p;
  }
}(Object.create(null)), {category:"total",months:{}});

console.log(result);

// now push this to data
data.push(result);

// console.log(data);

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

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