Create new objects based on shared property in previous array of objects

Question

I have an array of objects containing a "year" key and a "date" key like so:

    var fullDates = [
{ 'year': '2018', date: '2018-01'},
{ 'year': '2017', date: '2017-02'},
{ 'year': '2016', date: '2016-03'},
{ 'year': '2018', date: '2018-04'},
{ 'year': '2017', date: '2017-05' },
{ 'year': '2016', date: '2016-06'}
];

I want to make a new array of objects containing the year and the dates but where the "date" key is an array like shown below. How can i do this?

var final = [
{ 'year': '2018', date: ['2018-01', '2018-02']},
{ 'year': '2017', date: ['2017-03', '2017-04']},
{ 'year': '2016', date: ['2016-04', '2016-06']}
]

Possible duplicate of group objects in array based on value of key in object — cнŝdk
– cнŝdk, Commented Jul 16, 2018 at 13:54

Ankit Agarwal · Accepted Answer · 2018-07-16 13:45:24Z

1

You can use Array.reduce() operation to get that output:

var fullDates = [
  { 'year': '2018', date: '2018-01'},
  { 'year': '2017', date: '2017-02'},
  { 'year': '2016', date: '2016-03'},
  { 'year': '2018', date: '2018-04'},
  { 'year': '2017', date: '2017-05' },
  { 'year': '2016', date: '2016-06'}
];
var final = fullDates.reduce((acc, obj)=>{
  var existingObj = acc.find(item => item.year === obj.year);
  if(existingObj){
    existingObj.date.push(obj.date);
    return acc;
  }
  obj.date = [obj.date];
  acc.push(obj);
  return acc;
}, []);
console.log(final);

answered Jul 16, 2018 at 13:45

Ankit Agarwal

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2 Comments

bruno.almeida Over a year ago

hehe, same approach. beaten by 2min :). The only difference is that i don't change current object.

Ankit Agarwal Over a year ago

@fredd5229 glad to help.

cнŝdk · Accepted Answer · 2018-07-16 13:59:44Z

1

You can use array#reduce.

For each year, create an object containing year and dates properties and for each repeating year add date in the array. Then get all the values from this object accumulator.

const fullDates = [ { 'year': '2018', date: '2018-01'}, { 'year': '2017', date: '2017-02'}, { 'year': '2016', date: '2016-03'}, { 'year': '2018', date: '2018-04'}, { 'year': '2017', date: '2017-05' }, { 'year': '2016', date: '2016-06'} ],
    result = Object.values(fullDates.reduce((r, {year, date}) => {
      r[year] = r[year] || {year, dates : []};
      r[year].dates.push(date);
      return r;
    },{}));
console.log(result);

edited Jul 16, 2018 at 13:59

cнŝdk

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answered Jul 16, 2018 at 13:55

Hassan Imam

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Comments

bruno.almeida · Accepted Answer · 2018-07-16 13:47:54Z

0

Hope this helps:

    var fullDates = [
{ 'year': '2018', date: '2018-01'},
{ 'year': '2017', date: '2017-02'},
{ 'year': '2016', date: '2016-03'},
{ 'year': '2018', date: '2018-04'},
{ 'year': '2017', date: '2017-05' },
{ 'year': '2016', date: '2016-06'}
];



const reducer = (accumulator, currentValue) => {

    let yearData = accumulator.find(x => x.year == currentValue.year);
    if(yearData !== undefined){
        yearData.date.push(currentValue.date);
    }
    else{
        accumulator.push({ 'year': currentValue.year, date: [currentValue.date]});
    }


    return accumulator;
}


var final = fullDates.reduce(reducer, []);

answered Jul 16, 2018 at 13:47

bruno.almeida

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2 Comments

Ankit Agarwal Over a year ago

Your approach will need to know all the keys of the object in fullDates as you are creating a new object so that will add complexity if there are many properties in object.

bruno.almeida Over a year ago

That is absolutely true.

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