Javascript: Merging 2 or more Objects in the Same Array

Question

Any idea how to restructure a data structure like this

var data = [
  [{
    jan: 10,
    feb: 20,
    mar: 30,
    type: "one"
  },
  {
    jan: 20,
    feb: 10,
    mar: 40,
    type: "one"
  }],
  [
    {
    jan: 10,
    feb: 20,
    mar: 30,
    type: "two"
  },
  {
    jan: 20,
    feb: 10,
    mar: 40,
    type: "two"
  }]
]

console.log(data)

into something like this?

var data = [
  {
    jan: 30,
    feb: 30,
    mar: 70,
    type: "one"
  },
    {
    jan: 30,
    feb: 30,
    mar: 70,
    type: "two"
  }
]

console.log(data)

As seen in the example, objects in the same array are merged and the jan , feb and mar keys are added.

I'm at the end of my wits. Thanks in advance :)

You need to describe the merging rules more specific. As I can see, numbers are summed up. But what should happen to strings? Is it guarantied that they are the same for every object? — Larce
– Larce, Commented Jan 3, 2018 at 9:10
as shown above the strings or the type in every array they only have the same strings so strings will remain as it is after is simplified. — kcNeko
– kcNeko, Commented Jan 3, 2018 at 9:13

Rohit Agrawal · Accepted Answer · 2018-01-03 09:28:18Z

2

You can use map and reduce functions on javascript arrays to achieve your result.

Use map to iterate over the sub arrays inside your main array and use reduce inside those sub arrays to sum up the months data.

var data = [
  [{
    jan: 10,
    feb: 20,
    mar: 30,
    type: "one"
  },
  {
    jan: 20,
    feb: 10,
    mar: 40,
    type: "one"
  }],
  [
    {
    jan: 10,
    feb: 20,
    mar: 30,
    type: "two"
  },
  {
    jan: 20,
    feb: 10,
    mar: 40,
    type: "two"
  }]
]

var newData = data.map(function(arr){
  return arr.reduce(function(acc, ele, i){
    if(i === 0){
      acc = ele;
    }
    else{
      var keys= Object.keys(ele);
      keys.splice(keys.indexOf("type"), 1);
      keys.forEach(function(key){
         acc[key] += ele[key];
      })
    }
    return acc;
  },{});
});
console.log(newData)

edited Jan 3, 2018 at 9:28

answered Jan 3, 2018 at 9:20

Rohit Agrawal

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2 Comments

Nina Scholz Over a year ago

what do you do for other month's?

Rohit Agrawal Over a year ago

Hi @NinaScholz, updated my answer for variable months.

Nina Scholz · Accepted Answer · 2018-01-03 09:19:34Z

0

You could take a hash table for the object with the same type and add all values of properties which are not type.

var data = [[{ jan: 10, feb: 20, mar: 30, type: "one" }, { jan: 20, feb: 10, mar: 40, type: "one" }], [{ jan: 10, feb: 20, mar: 30, type: "two" }, { jan: 20, feb: 10, mar: 40, type: "two" }]],
    hash = Object.create(null),
    grouped = [];

data.forEach(function (a) {
    a.forEach(function (o) {
        if (!hash[o.type]) {
            hash[o.type] = { type: o.type };
            grouped.push(hash[o.type]);
        }
        Object.keys(o).forEach(function (k) {
            if (k === 'type') {
                return;
            }
            hash[o.type][k] = (hash[o.type][k] || 0) + o[k];
        });
    });
});

console.log(grouped);

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

answered Jan 3, 2018 at 9:19

Nina Scholz

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1 Comment

Rajesh Dixit Over a year ago

Please choose to close such question as duplicate instead.

gurvinder372 · Accepted Answer · 2018-01-03 09:28:52Z

Use reduce and forEach

var output = Object.values( data.reduce( function( a, c ){
  c.forEach( function( item ){
     a[ item.type ] = a[ item.type ] || { jan: 0, feb: 0, mar: 0, type: item.type };
     a[ item.type ].jan += item.jan; 
     a[ item.type ].feb += item.feb;
     a[ item.type ].mar += item.mar;
  });
  return a;
}, {}));

Demo

var data = [
  [{
    jan: 10,
    feb: 20,
    mar: 30,
    type: "one"
  },
  {
    jan: 20,
    feb: 10,
    mar: 40,
    type: "one"
  }],
  [
    {
    jan: 10,
    feb: 20,
    mar: 30,
    type: "two"
  },
  {
    jan: 20,
    feb: 10,
    mar: 40,
    type: "two"
  }]
];

var output = Object.values( data.reduce( function( a, c ){
  c.forEach( function( item ){
     a[ item.type ] = a[ item.type ] || { jan: 0, feb: 0, mar: 0, type: item.type };
     a[ item.type ].jan += item.jan;
     a[ item.type ].feb += item.feb;
     a[ item.type ].mar += item.mar;
  });
  return a;
}, {}));

console.log(output);

Hassan Imam · Accepted Answer · 2018-01-03 09:43:18Z

0

You can use array#reduce to group your data based on the type value. Use array#forEach to iterate through each array.

var data = [ [{ jan: 10, feb: 20, mar: 30, type: "one" }, { jan: 20, feb: 10, mar: 40, type: "one" }], [ { jan: 10, feb: 20, mar: 30, type: "two" }, { jan: 20, feb: 10, mar: 40, type: "two" }] ];
var result = Object.values(data.reduce((r,a) => {
  a.forEach(o => {
    r[o.type] = r[o.type] || Object.assign({'type': o.type});
    Object.keys(o).forEach(k => {
      if(k !== 'type')
        r[o.type][k] = (r[o.type][k] || 0) + o[k];
    });
  });
  return r;
},{}));

console.log(result);

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

edited Jan 3, 2018 at 9:43

answered Jan 3, 2018 at 9:31

Hassan Imam

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Comments

Shanon Jackson · Accepted Answer · 2018-01-03 23:22:45Z

0

data.reduce((a,c) => {
    return a.concat(c.reduce((a2,c2) => {
        if(Object.keys(a2).length === 0) return c2;
        return Object.assign({}, a2, {jan: a2.jan + c2.jan, feb: a2.feb + c2.feb, mar: a2.mar + c2.mar})
    },{}))
},[])

Nested reduce fully immutable solution.

answered Jan 3, 2018 at 23:22

Shanon Jackson

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