Grouping with sum of a key value in JavaScript array of object

Question

I have an array of object like below

var data = [{monthName: "Jun", name:'web', number: 1, month: 6}, 
{monthName: "Jul", name:'web', number: 2, month: 7},
{monthName: "Aug", name:'web', number: 2, month: 8}, 
{monthName: "Jun", name:'sales', number: 12, month: 6}, 
{monthName: "Jul", name:'sales', number: 2, month: 7}]

I want to group the data based on key "name" and then need to get the number as an array.

Sample output like below

datasets: [{
     name: 'web',
     number: [1, 2, 2],
       },{
    name: 'sales',
    number: [12, 2]
         }]

I am not sure about how to group data and then get a key value as array.

I have grouped the data using below code

result = data.reduce(function (r, a) {
             r[a.name] = r[a.name] || [];
             r[a.name].push(a);
        return r;
    }, Object.create(null));

But not sure about how to get the desired output. Can someone help me ?

Jonas Wilms · Accepted Answer · 2019-08-20 17:18:43Z

1

While reducing, also build up the wanted result objects if the key doesn't exist yet:

  const result = [];
  { // Make hash viable to GCing after this operation
    const hash = Object.create(null);
    for(const { name, number } of data) {
       if(!hash[name])
         result.push({ name, numbers: hash[name] = [] });
       hash[name].push(number);
    }
  }

edited Aug 20, 2019 at 17:18

answered Aug 20, 2019 at 17:14

Jonas Wilms

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4 Comments

Arunprasanth K V Over a year ago

is there any way to get the iteration number also in this example ?I mean here we have two objects in the array so the first object's iteration number will be 1 and second one's will be 2 like that ?

Arunprasanth K V Over a year ago

hi the given solution is counting in each steps, i mean for the first item it is coming as 0 as index and for the next item its 3 because the inner loop for creating the number [] also counts here

Jonas Wilms Over a year ago

Ah, at the end do result.forEach((entry, index) => Object.assign(entry, { index })), but its unclear why you need that, I mean you can easily get the index with .indexOf

Arunprasanth K V Over a year ago

no problem i have just used result.length inside, solved the issue . thanks for the wonderful solution

Taki · Accepted Answer · 2019-08-20 17:15:24Z

you'll need to check if the array has an object with the name , if it does, append the number to it, otherwise push a new object :

var data = [
  { monthName: "Jun", name: "web", number: 1, month: 6 },
  { monthName: "Jul", name: "web", number: 2, month: 7 },
  { monthName: "Aug", name: "web", number: 2, month: 8 },
  { monthName: "Jun", name: "sales", number: 12, month: 6 },
  { monthName: "Jul", name: "sales", number: 2, month: 7 }
];

var result = data.reduce((acc, curr) => {
  const ndx = acc.findIndex(e => e.name === curr.name);

  if (ndx > -1) {
    acc[ndx].number.push(curr.number);
  } else {
    acc.push({
      name: curr.name,
      number: [curr.number]
    });
  }

  return acc;
}, []);

console.log(result);

claasic · Accepted Answer · 2019-08-20 17:25:59Z

Create a map which groups the entries with reduce, then get the entries of the map with Object.entries and iterate over them with map, creating a new object for each in the process.

var data = [{monthName:"Jun",name:"web",number:1,month:6},{monthName:"Jul",name:"web",number:2,month:7},{monthName:"Aug",name:"web",number:2,month:8},{monthName:"Jun",name:"sales",number:12,month:6},{monthName:"Jul",name:"sales",number:2,month:7}];

function mergeName(arr) {
  let map = data.reduce((a,c) => (a[c.name] = ({...c, 
            number: a[c.name] && a[c.name].number
                    ? a[c.name].number.push(c.number) && a[c.name].number 
                    : [c.number]}),a),{});
  return Object.entries(map).map(o => ({name: o[0], number: o[1].number}))
}

console.log(mergeName(data))

junvar · Accepted Answer · 2019-08-20 18:22:35Z

1

You're answer is almost correct, just add an additional line to push to a number array:

var data = [{monthName: "Jun", name: 'web', number: 1, month: 6},
	{monthName: "Jul", name: 'web', number: 2, month: 7},
	{monthName: "Aug", name: 'web', number: 2, month: 8},
	{monthName: "Jun", name: 'sales', number: 12, month: 6},
	{monthName: "Jul", name: 'sales', number: 2, month: 7}];

result = Object.values(data.reduce(function (r, {name, number}) {
	r[name] = r[name] || {name, number: []};
	r[name].number.push(number);
	return r;
}, {})).map((v, i) => ({...v, iteration: i + 1}));

console.log(result);

edited Aug 20, 2019 at 18:22

answered Aug 20, 2019 at 17:18

junvar

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1 Comment

Arunprasanth K V Over a year ago

is there any way to get the iteration number also in this example ?I mean here we have two objects in the array so the first object's iteration number will be 1 and second one's will be 2 like that ?

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