Combine the attributes of an array of objects in Javascript

Question

I have this dataset:

var dataset = [
{time: "t1", val1: 0, val2: 0, val3: 1},
{time: "t2", val1: 0, val2: 0, val3: 4},
{time: "t3", val1: 1, val2: 0, val3: 0},
{time: "t4", val1: 3, val2: 0, val3: 0},
{time: "t2", val1: 0, val2: 3, val3: 0},
{time: "t4", val1: 0, val2: 2, val3: 0},
{time: "t5", val1: 2, val2: 0, val3: 0},

....
];

I want to reduce the dataset to uniques time entries but also combine the values per timestep. The result must look like this:

var dataset = [
{time: "t1", val1: 0, val2: 0, val3: 1},
{time: "t2", val1: 0, val2: 3, val3: 4},
{time: "t3", val1: 1, val2: 0, val3: 0},
{time: "t4", val1: 3, val2: 2, val3: 0},
{time: "t5", val1: 2, val2: 0, val3: 0},
....
];

I tried someting with the reduce() method based on other SO posts:

dataset.reduce(function(r,o){
var key = o.Date;
var newObj = o;
if (r[key] || (r[key]=[])) r[key].push(o);
  return r;
}, []);

console.log(dataset);

It reduces the dataset to 5 entries, but the structure isn't exactly how I want it and I don't know how to combine the object values.

Any help is appreciated.

What if there would be three t3 objects and two of them contain e.g. val2 property. Which one should be used? — Ivan Sivak
– Ivan Sivak, Commented Sep 29, 2017 at 14:38

RomanPerekhrest · Accepted Answer · 2017-09-29 14:44:37Z

4

Array.reduce() variation:

var dataset = [
    {time: "t1", val1: 0, val2: 0, val3: 1}, {time: "t2", val1: 0, val2: 0, val3: 4}, 
    {time: "t3", val1: 1, val2: 0, val3: 0}, {time: "t4", val1: 3, val2: 0, val3: 0}, 
    {time: "t5", val1: 2, val2: 0, val3: 0}, {time: "t2", val1: 0, val2: 3, val3: 0}, 
    {time: "t4", val1: 0, val2: 2, val3: 0}
],
result = [];

dataset.reduce(function(r, o){
   var k = o.time;   // crucial key (used for grouping entries)
   if (r[k]) {
       r[k].val1 +=o.val1;
       r[k].val2 +=o.val2;
       r[k].val3 +=o.val3;
   } else {
       result.push(o);
       r[k] = o;
   }
   return r;
}, {});

console.log(result);

edited Sep 29, 2017 at 14:44

answered Sep 29, 2017 at 14:39

RomanPerekhrest

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Comments

Adam · Accepted Answer · 2017-09-29 14:51:49Z

You can save the time values on each iteration step into a temporary keys property:

var dataset = [
    { time: "t1", val1: 0, val2: 0, val3: 1 },
    { time: "t2", val1: 0, val2: 0, val3: 4 },
    { time: "t3", val1: 1, val2: 0, val3: 0 },
    { time: "t4", val1: 3, val2: 0, val3: 0 },
    { time: "t5", val1: 2, val2: 0, val3: 0 },
    { time: "t2", val1: 0, val2: 3, val3: 0 },
    { time: "t4", val1: 0, val2: 2, val3: 0 },
];

var newData = dataset.reduce(function (r, o) {
    if (r.keys[o.time] !== true) {
        r.data.push(o);
    }
    r.keys[o.time] = true;
    return r;
}, { data: [], keys: {} }).data;

console.log(newData);
//[ { time: 't1', val1: 0, val2: 0, val3: 1 },
//  { time: 't2', val1: 0, val2: 0, val3: 4 },
//  { time: 't3', val1: 1, val2: 0, val3: 0 },
//  { time: 't4', val1: 3, val2: 0, val3: 0 },
//  { time: 't5', val1: 2, val2: 0, val3: 0 } ]

You aren't updating anything. It appears that you are just keeping the first time and getting rid of the duplicates.

Renzo Calla · Accepted Answer · 2017-09-29 14:47:34Z

You can use Array methods like the example

var dataset = [
{time: "t1", val1: 0, val2: 0, val3: 1},
{time: "t2", val1: 0, val2: 0, val3: 4},
{time: "t3", val1: 1, val2: 0, val3: 0},
{time: "t4", val1: 3, val2: 0, val3: 0},
{time: "t5", val1: 2, val2: 0, val3: 0},
{time: "t2", val1: 0, val2: 3, val3: 0},
{time: "t4", val1: 0, val2: 2, val3: 0}
];

var datasetReduced=[];

dataset.forEach(function(dataItem){
  var reducedItem = datasetReduced.find(function(element){
    return element.time === dataItem.time;
  });
  if(reducedItem){
    
    reducedItem.val1= reducedItem.val1 + dataItem.val1;
    reducedItem.val2= reducedItem.val2 + dataItem.val2;
    reducedItem.val3= reducedItem.val3 + dataItem.val3;
  }else{
    datasetReduced.push(dataItem);
  }
});
console.log(datasetReduced);

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