how to bundle objects in an array by date attribute

Question

I have a big array with data. Here is a example of the structure:

let data = [
  {
    date: '2018-11-22',
    values: {
      a: 10,
      b: 20,
      c: 5,
    },
  },
  {
    date: '2018-11-17',
    values: {
      a: 5,
      b: 10,
      c: 15,
    },
  },
  {
    date: '2018-06-29',
    values: {
      a: 10,
      b: 30,
      c: 10,
    },
  },
  {
    date: '2017-12-20',
    values: {
      a: 30,
      b: 40,
      c: 5,
    },
  },
];

I need this data structured in a new array by month and year. The value attributes should be summed up for each month.

So the new array for the example should look like this:

let sortedData = [
  {
    date: '2018-11',
    values: {
      a: 15,
      b: 30,
      c: 20,
    },
  },
  {
    date: '2018-06',
    values: {
      a: 10,
      b: 30,
      c: 10,
    },
  },
  {
    date: '2017-12',
    values: {
      a: 30,
      b: 40,
      c: 5,
    },
  },
];

I'm trying for hours to write a working function but I can't handle it. Any ideas how I can bundle an array like this?

Thanks for your help!

Nitish Narang · Accepted Answer · 2018-11-29 16:11:15Z

4

You can use Array.reduce for this

let data = [  {    date: '2018-11-22',    values: {      a: 10,      b: 20,      c: 5,    },  },  {    date: '2018-11-17',    values: {      a: 5,      b: 10,      c: 15,    },  },  {    date: '2018-06-29',    values: {      a: 10,      b: 30,      c: 10,    },  },  {    date: '2017-12-20',    values: {      a: 30,      b: 40,      c: 5,    },  },];

let res = data.reduce((o, {date, values}) => {
  let k = date.slice(0, 7)
  
  o[k] = o[k] || {date: k, values: {a: 0, b: 0, c:0}}
  o[k].values.a += values.a
  o[k].values.b += values.b
  o[k].values.c += values.c
  
  return o
}, {})

console.log(Object.values(res))

answered Nov 29, 2018 at 16:11

Nitish Narang

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2 Comments

iamrobin. Over a year ago

Is there a way to bundle months in an array and not in an object?

Nitish Narang Over a year ago

@iamrobin. Yes possible. Can you pls tell expected output?

Akrion · Accepted Answer · 2018-11-30 02:59:08Z

1

You can also do make it more concise and not deal with the individual values props like this:

let data = [{ date: '2018-11-22', values: { a: 10, b: 20, c: 5, }, }, { date: '2018-11-17', values: { a: 5, b: 10, c: 15, }, }, { date: '2018-06-29', values: { a: 10, b: 30, c: 10, }, }, { date: '2017-12-20', values: { a: 30, b: 40, c: 5, }, }, ];

const result = data.reduce((r, {date, values}) => {
  date = date.substr(0,7)
  r[date] = r[date] 
   ? (Object.keys(values).forEach(k => r[date].values[k] += values[k]), r[date])
   : {date, values}
  return r
}, {})

console.log(Object.values(result))

This way you would not care if there are 3 of 10 properties in values and you get more generic solution.

edited Nov 30, 2018 at 2:59

answered Nov 30, 2018 at 2:39

Akrion

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